Hydrokinesis! Itās finally here! Iāve had this one on the backburner for just over 2 months now so this one may be a bit all over the place, but we push through regardless.Ā
Now to start with we have the basic overview, with hydrokinesis weāre looking at a seemingly simple telekinesis quirk thatās specialized for water. Its user, Mitzuki, is capable of all manner of things with it, being able to sense, control, and eventually change the phase of nearby water, though it comes at a cost to their energy with fatigue and aches after use. Similar to Hardening or Electrification itās a simple quirk that can become Very powerful with training and creativity. But thatās not what weāre here for, weāre here to see what makes this quirk tic. I didnāt do a great job on that front but I do have some ideas.
First off we have to figure out how exactly Mitzuki is sensing nearby water. Briefly touching on what we know of this aspect of his quirk we know Mitzuki can roughly tell where water is located, including when itās hidden or bonded to something like in blood, salt water, or (hypothetically) certain types of rocks, so long as it makes up at least 30% of the objectās volume/mass. The range of this sensing ability is marked at about 45 feet in a radius around Mitzuki, which indicates a spherical range, as is common for telekinetic quirks. As mentioned earlier this ability isnāt impeded by any objects between the user and the targeted water, and stray energy like fire barely affects it. This is VERY interesting as it means that whatever ability is being used here isnāt reliant on quirk magic telekinesis since otherwise the previously mentioned limit of 30% would be much different. It would likely be looking at roughly 50% water required since thatās the line where it becomes less āwater with attached materialā and more āobject with water insideā. Alternatively it could be near impossible to use water with any degree of bonding to other substances like salt as itās no longer technically āwaterā anymore, and if it Could and it doesnāt care about the 50% threshold then 30% wouldnāt make much sense either, since the quirk seems to be precise enough to target much smaller concentrations and would be pulling from resources closer to the 90-99% ranges. Of course it could be a matter of telekinesis just not being very precise and operating off of quirk magic so the percentage just happens to land there, but I like to reduce quirk fuckery wherever possible.
So if weāre not going with the obvious telekinesis what Are we going with? Well after a solid month of hypothesizing and researching Iāve landed on two potential ideas, a pulse system or a magnetic field (sorry compound based chemical reaction, you were interesting but fated to be relegated to an honorable mention from your conception in the early drafts).
A pulse system would look very similar to echolocation, having Mitzuki send out pulses of something (likely some kinda electrical, vibration, or telekinetic based pulse) and waiting for it to bounce back. From there any changes in direction, speed, and strength could be used to tell what materials are where, though the exact mechanics would depend on what the pulse is based off of. Unfortunately while better than the vast majority of ideas this still comes with a number of problems. After pouring over ideas the earlier three pulse types have the least issues, and they still have some pretty serious drawbacks. For electrical pulses all manner of insulating or conductive materials would cause massive problems with telling whatās where, and would fall apart when confronted with a secondary shock, all on top of being near useless in the air. Vibration based pulses are better, but still face issues with air based detection, needing hypersensitive detectors or near concussive blasts to get any sort of useful information. Telekinesis has the best chance but many of the previously mentioned issues with telekinesis being over or under specialized crop back up.
The other, much more likely, option is a long standing favorite of mine, magnetic fields. To horrifically oversimplify, magnetic fields are a semi-spherical area between two magnetic poles (usually a magnet or rapidly spinning metal) that are affected by the force of magnetism. They get very complicated very quickly and I go into more detail in Blood Supernova, but for now just know that on top of being magnetic (or maybe because of? I havenāt looked at my old research in over a month and physics is hard) they have a minor effect on all sorts of matter and energy that goes through them. The effect is minor enough that aside for very very dense materials or very very high energy particles pretty much nothing but other magnets does more than slightly react to them, allowing for an undisturbed range. On top of that almost all matter is magnetic to some degree, but water is whatās known as diamagnetic, AKA one of the few materials actually pushed away by magnetism instead of drawn in. This means that by sensing disturbances in the magnetic field Mitzukiās brain can automatically tell whatās water by how it reacts to the field. Now presumably water stuck in or bonded to other materials would react differently, but by comparing the expected reaction to what actually happens the body can roughly tell āthereās X amount of water hereā and log it accordingly. This route would also help explain the loss of control the further away water gets, since magnetic fields get weaker the further out they go from their source, which is directly reflected in Mitsukiās relative control over water compared to its distance from him. Also as another step up from the pulse system magnetic fields are roughly spherical and unimpacted by air or walls, which are the major hang ups of any decent detection system. Unfortunately they would still be impacted by magnetic or electric quirks, but that can be somewhat circumvented by Mitzukiās greater control over visible water indicating that once detected, telekinetically held water can still be moved around separate from the magnetic field. Still an issue, but I can only do so much without quirk magic okay. They would also face serious issues getting past certain superconductors as they would block the field past them, though if small enough theyāre likely to be pulled in, bypassing the issue (not to mention such materials are rare and expensive, so theyāre unlikely to be a common issue).
If we follow the magnetic field idea itās unclear if the whole thing is constant or a startup thing. If itās constant then the body has to have some sort of specialized organ that can house a powerful magnet, or utilize a number of smaller magnets across the body. Though that route would have some difficulty as conflicting magnetic fields can cause issues, so overall a single powerful source is more likely. In the case of a startup system the same principle applies, but the organ would need to be altered. Instead of a solid chunk of magnet it would be better to distill metals from mineral rich foods into a magnetic slurry thatās brought together into a single whole during quirk activation, but otherwise kept as separate smaller magnets. Personally I find the constant magnet much more likely, with Mitzuki either just constantly sensing water sources or automatically filtering out the information when not focusing on it, similar to peripheral vision.
As a side note, while certainly powerful, Mitzukiās magnetic field is still leagues behind the likes of Blood Supernova, so many of the benefits and issues associated with it arenāt as extreme, or even applicable at all in some cases. At worst I see Mitzuki having issues with cheaper electronics that might not have the same standard protections for rogue magnetic and electric quirks, likely in the form of glitches and the occasional bit of data loss. Next up!
So Mitzuki is moving a good amount of water pretty easily and with almost no requirements or added effects besides needing to visualize the movement. Pretty useful but unfortunately it means that despite my greatest protests Iāll have to concede the point to quirk magic. Mitzukiās hydrokinesis is in fact a purely quirk magic water based telekinesis. Still keeping the water detection system in though, I had good ideas there and Iām not giving them up without a fight.
How does telekinesis work anyways? Well, thereās certainly a few routes to go with, but taking into account the needed visualization my bet is that itās simple āmove a chunk of space in this way, guided by how I see it goingā. As things are right now itās pretty basic, just being sections of water being moved around in unique ways. But with training (or a mini/full awakening) this could be narrowed down for more precise control.Ā
Aside for the obvious with tiny streams of water, needle-like movements, and being able to coat objects in an imperceptible small layer of water (useful for finding the layout of a building or picking a lock) other options are available as well. The difference between ice, water, and steam is the molecules formation and energy level, both of which can be controlled through telekinesis. By intentionally moving the molecules quickly theyāll become higher energy, forming steam, and on the other end of the spectrum by holding them still in the right shape ice will quickly form. This will require a lot more skill as itās more of an automatic process rather than the intentional movements currently being done, but it is possible and likely to become easier with practice.Ā
Interestingly ice and steam are likely to be a bit harder to detect as theyāre less dense than liquid water, but it wont be overly noticeable. More importantly will be the difficulty in controlling them, as they both operate at a very different energy level than Mitzuki is used to, and without proper training itās likely theyāll accidentally be moved around too much or too little and melt/condense. With proper training though being able to utilize all three water phases simultaneously will be a massive boon, using steam to stealthily spread water across the area, moving water around and forming ice at the moment of contact to condense the force of the strike down to a single spot, slipping steam into tiny water-tight holes and quickly forming ice to crack them open. Simple quirks often have quite a lot that can be done with them with some creativity.
As a side note thanks to physically holding the water down to the molecular level it likely has a much higher surface tension than would be expected, making moving through the stuff like crawling through molasses as long as Mitzuki doesnāt accidentally visualize the water moving around the person inside (this would also render ice far harder and steam feel like a thick fog despite being much thinner. Interestingly steam is actually going to look pretty weird since it wont react to all the little air currents and natural movements it usually has). It also means that Mitzuki gets to play a fun game of physics, moving large amounts of mass at high speeds, especially if he focuses down to a single point since having such a high surface tension removes much of the give that makes being hit by water safe.Ā
Speaking of water physics, a quick rundown has Mitzuki moving approximately 3X his body's mass/volume of water at 2-3 times the speed of his movement. These limits are interesting since they imply an issue with either quirk strength or energy efficiency, both of which could be pushed through during times of stress but donāt have easy ways to train up normally outside of just using the quirk, though weather that increase is shown as a steady gain over the months of school or rapid gains during intense training is completely unpredictable. As a side note by the way I tried running the numbers and either I screwed up the math or humans have like no volume, so itās probably better to just eyeball amounts and call it a day than continue my quest to physics my way to insane numbers.
While a telekinetic quirk doesnāt at first seem very body focused it gets a bit more interesting when looking into Mitzukiās quirk drawbacks, namely the fatigue and full body ache that comes with overuse. This would indicate that its drawing from the body somehow, likely some sort of energy source to power the high demands of a telekinesis quirk. This is most likely to either be some sort of new, secondary energy source Mitzukiās body naturally produces, likely at the cost of regular energy, or itās using the body's natural energy (ATP) as fuel.
A secondary energy type to draw from would leave the body some slack during overuse, allowing Mitzuki to function even when fully drained quirk wise, though it would be at the cost of having less overall energy for quirk use.
While most energy based quirks use a secondary source I actually believe the natural energy route is more likely, though it would require a massive base energy requirement which Iāll touch on later. For now though, know that Mitzuki would be burning through his body's natural energy every time he tries to move some water around (likely proportional to the amount being moved and how much inertia is being overcome), leaving him far more drained than a standard energy quirk would. Luckily for Mitzuki, ATP is produced in humans in two main ways depending on how much oxygen is being received, aerobic and anaerobic respiration. Aerobic is what we usually use, turning oxygen and glucose (sugar) into about 32 ATP per glucose. Meanwhile anaerobic respiration uses glucose but only makes about 2 ATP per glucose, though in exchange itās a far faster process that doesnāt need any oxygen to run. As a side effect of anaerobic respiration lactic acid is also produced, which is a major part of why when you exercise too much you might experience pain in your side as it turns out the human body isnāt a fan of having acid near your muscles.
So why go into all of that? Well mainly for later mutations, but also because it means that while the body is using its own energy for quirk use, itās not necessarily restrained by normal production limits and could either make use of mutations for better oxygen efficiency or a much higher glucose intake/efficiency to have a much higher base energy supply. It could also make use of anaerobic respiration to make quick energy on the fly with just food, bypassing the limits normally imposed by lung capacity, oxygen transport times, and respiration times, especially if itās combined with the fast digestion weāll go over later to be able to utilize food that was eaten right before a fight as well as the standard levels. Itās also possible that, just like we have the joy of anaerobic respiration in our sides when running in the form of āstitchesā, Mitzuki could have certain areas default to anaerobic respiration to maintain oxygen supplies elsewhere for more efficient ATP production in areas that really need it like the brain, legs, and magnetic organ.
As a side note this would mean that for Mitzukiās drawback fatigue (low energy) is likely to crop up first, but the aches and pains would show up during faster fights when tons of energy is needed without giving him time to get all the oxygen needed to power such levels.
Now itās worth noting that all this stuff about magnetic fields and energy requirements are likely going to have a massive impact on Mitzukiās diet. Metal rich foods are a requirement for forming magnets of course, but for energy carbohydrates are king. Simple carbs like sugars and certain foods like frys give fast energy, especially in the case of a faster metabolism/digestion speed, while complex carbs like fruits and certain breads are great for energy over a longer time frame, especially for slower metabolisms/digestion speeds (by the way you would not believe the amount of diet ads and scare tactics I came across while researching for this little bit. Diet culture is scary man).
Every quirk comes with mutations, usually classified as Supporting (help the quirk), Vestigial (inherited), or Cosmetic (new mutation with no effect on quirk). In Mitzukiās case heās likely to have a mental mutation to have better spatial awareness and multitasking capabilities than in baseline humans so he can better visualize his water, as opposed to baseline humans only being able to focus on one thing at a time. How difficult holding and moving a proper image in his mind is is unclear, but similar to quirks, mutations can also grow and adapt so it should become easier with training.
Moving on to the magnetic field idea from earlier, the magnetism needed for such a large field would be intense and likely wreck havoc on a normal human body. Luckily the average person in MHA can easily body hits that shatter concrete and shake off lethal shocks on the daily, so your average person is probably fine. Mitzuki however is still in the center of his magnetic field where the effects are strongest. For the average organ this isnāt a big deal, but the highly magnetic blood moving throughout his body is a different story. Luckily this could be remedied by cheating off of Blood Supernovas solution and pulling from the magnet organ to put tiny magnets in each blood cell (though this would mean Mitzuki needs even more metal in his diet), giving each cell its own mini-magnetic field. These magnetic fields would be small enough to not interfere with the larger field, but still protect the cell inside from getting dragged along, though they would likely have to spin to even out the attraction-repulsion each side would experience. Alternatively the magnetism could be made useful, with arteries giving/taking electric charge from passing blood, drawing and pushing them around the body (this would be particularly useful if the magnetic organ was split to have two major fields on the top and bottom of the body). Now this is very very handwavy, to the point I considered just removing it entirely, but it could be helped along via automatic hydrokinesis pushing blood along, with the magnetic fields just being there to help things along (or more likely being absent entirely).
Now to switch gears we can jump back to energy requirements. These are likely to be handled one of three ways, fast, standard, or slow metabolism. If the body is looking to restore energy quickly itās going to need much faster digestion than in baseline humans, allowing for quick energy at the cost of being super inefficient. This would leave Mitzuki needing tons of food throughout the day and going hungry very fast, likely leading to snacking throughout the day instead of the standard 3 meals most people have. This route could also potentially lead to mini-energy spikes in the half hour or so after snacking, followed by a short period of low energy as the body runs out of food. Mitzuki is also rather likely to have major fluctuations in his fat concentrations, requiring large amounts of energy during sleep, or having his body shut down non-essential functions during sleep. Almost like hibernation, but only cropping up when the body decides it needs to rest (such as after a major fight or when up for too long) so it can process fat and recover. Going the standard route, energy processing will be very similar to baseline humans, if needing more food than normal. Some basic mutations like a larger stomach and more efficient movement instincts are likely, but overall not too noticeable. Finally if the body decides the best way to meet energy requirements is efficiency itās likely to go the slow route, utilizing a much slower digestion process. This would allow Mitzuki to truly make the most out of his food, likely only needing a single large meal each day and slowly digesting it throughout the day, proving a constant stream of low energy instead of the normal peaks and valleys (minus a likely dip at night as the body tries to sleep, and doesnāt need so much energy). While a generally low energy route, Mitzuki still needs to be active, so itās likely the body will up the allotted energy when heās emotional, moving a lot, or having an adrenaline rush. This extra energy could be made up for through leftover fat, which would likely be easily put on as this body plan is so much more focused on the threat of starvation. Now each of these methods would most likely be incompatible, that kinda switching around in the body plan usually requires a transformation quirk, but some of the listed mutations could easily be carried over to other routes.
To continue on energy efficiency we go back to oxygen. Since the main issue Mitzuki is likely to face when it comes to oxygen is not getting enough of it, most mutations would look to cover that issue. Stuff like larger lungs, a more robust circulatory system, and rerouted veins to bring more oxygen to high-energy areas would all be quite helpful. On the more extreme end (likely requiring a mutation quirk somewhere in the ancestry, or be a multi-generation supporting mutation that's had time to develop) we have stuff like the air pockets some birds use, allowing for the storage of near pure oxygen. These would be a hazard though as pure oxygen is quite corrosive and flammable, not to mention each pocket would either need to siphon into the main lungs or have their own set of independent mini-lungs to pick up slack when the body starts to run low. Either way any of these mutations would have some minor consequences, such as not being able to hold his breath for long on such an oxygen dependent system and being extra buoyant, but the extra energy efficiency they provide more than makes up for those smaller details.
(Mostly) Moving past the energy requirements we have Mitzukiās sweat, which has canonically been buffed up (wait checked and he has fast metabolism, so that whole section on energy efficiency was kinda pointless. Oh well it gets to stay in cause I like it) to provide more water he can use. This is a pretty standard mutation but it also serves to show his body is pretty well adapted to his specific quirk, likely due to his parentage. Also means he needs a lot more sodium in his diet, which is really just another thing to tack on to the ever growing list of dietary requirements Mitzuki is amassing.
Speaking of parentage weāve finally reached the vestigial mutations! Thanks to Mitzukiās father (an elemental quirk covering air, water, earth and fire) thereās a pretty wide array of options open to him (less so on his mothers side due to her quirk status, but any persistent vestigial mutations from her side of the family are likely to stick if they made it onto her). While what specifically transfers over is up for debate, some of the more useful bits and bobs are very likely to get snagged, specifically some of the adaptations for the air and water elements. Air is likely to provide a base for the earlier oxygen efficiency, with Mitzuki having a much more efficient version as the quirk picks out what does and doesnāt work. The air pocket idea in particular would require its start in either Mitzukis father or (more likely) his grandparents, likely as a way to store useful air elements like oxygen, carbon dioxide, and even more dangerous stuff like sulfur and carbon monoxide (which in Mitzuki is likely to either not pass on, naturally leak out with his breath as the body doesnāt have its previous release mechanisms, or be completely transformed into oxygen refinement and storage). Water meanwhile would form the basis of Hydrokinesis with stuff like the increased sweat production, potentially a natural inclination for wet areas or the sound of moving water (white noise my beloved), better visualization, and the early stages of whatever method is used to find and target water specifically (though the addition of other elements makes the magnetic field system more likely as fire and stray molecules in the air are still detected by magnetic fields but would struggle to be detected by a pulse system). Earth could provide useful features like a sensitivity to how different materials react to the sensing method being used, which in earth would be a way to tell different rocks apart, but in Hydrokinesis would be the basis of picking out water within other materials, as well as generally increase Mitzukiās precision. Lastly fire is technically the least useful of the bunch, but has some pretty unique mutations. Whereas most of the others could pretty feasibly be attributed to any of the other elements, these would include the potential for things like an extra eyelid/membrane (to keep out smoke and prevent dry eye), much thicker cilia/mucus in the throat/lungs to limit smoke damage, thicker skin to prevent dangerous burns (though this would likely come at a cost of being less sensitive to touch), extra thermoregulation within the body (potentially some kinda coolant that can be released when overheating, or a way to transfer heat to the lungs/throat where it can be exhaled, though this would be far less efficient without the pyrokinesis of Mitzukiās father), which help lay the basis of Mitzukiās higher sweat production just as much as the water did, and lastly specialized pupils that could expand/retract in response to light levels as fireās quick flashes of light would otherwise cause some pretty annoying long term damage, on top of temporarily blinding the user if the fireās sufficiently brighter than the surroundings. These mutations may not be as immediately useful, but their more defensive nature means they might get snagged anyways as purely vestigial mutations.
Now I originally didnāt plan on going past the biological section, but Mitzuki just has so much potential I couldnāt help myself, so congrats on getting some extra here.
So thanks to having a very high base energy level Mitzuki is likely to have a pretty easy time training, not suffering from exhaustion nearly as quickly as his classmates, allowing for more total training (though in return quirk training is likely to feel far harder relative to physical training). On top of that thanks to his main drawback being fatigue and pain Mitzuki is likely to have a much higher natural pain tolerance, either due to a mental mutation or simply training his quirk pre-UA leading to being able to compartmentalize it.
Itās also worth considering the fact that quirks adapt and grow in response to training, and in Mitzukiās the obvious routes are in his magnetism and telekinesis. In the case of strengthening his magnetic field Mitzuki would need to try practicing his fine control or move lots of water near the edge of his range, indicating to his quirk growth is needed there. The easiest way for the quirk to grow to support these new needs would be to up the strength of the magnetic field, leading to better fine control closer to the center and a wider range at the ends. Unfortunately this is likely to lead to some issues, like making cheaper electronics near unusable and even standard stuff occasionally glitch or lose data (though higher quality stuff is likely to do just fine) or some initial pain as the magnetic organ needs to either become denser or larger and the body needs some time to adjust (this would also lead to higher energy and metal requirements). The telekinesis aspect is a bit more nebulous but would reasonably train in a similar way. I imagine its natural growth would be more towards fine control than weight, eventually leading to some control over the natural movement of water. This could then be manipulated to increase/decrease its movement, and thus its energy. Messing with the energy of the water would allow for the formation of ice/steam, though actual control over this process would require its own set of personalized training so it becomes more automatic. Of course training for both routes would be needed for better control over bonded water, with a stronger magnetic field being needed to sense smaller amounts of water, and a more precise telekinesis to actually pull it out.
Now to dive into the meat of this section, the support gear. Obviously having water on hand is useful, but anything beyond that would really depend on how Mitzuki wants to form his hero persona and specializations. On the offensive side of things he has mid-range combat well covered, but close range combat requires a reaction time his water simply doesnāt seem capable of while relying on visualization without significant reaction time training. Though of course if he does reach that point Mitzukiās higher control over closer water would make close range combat and defense a null issue. Until then some sort of knuckles or bladed weapon would be a pretty good fit for most costumes, though it could be modified to be hollow so it can be filled with water, allowing for Mitzuki to track and control it when needed as well as add on speed to its movement if he reacts fast enough (though it would require some training to get used to, and having less mass means that if he doesnāt use hydrokinesis itāll have less force then normal). This would be especially useful if by giving it a container Mitzuki only needs to focus on making the water move, rather than thinking up a specific shape and path, allowing for actual control without wasting time on details. In fact if this works it might be worth going with a sleeker, needle like design, rather than a typical knife or sword (assuming it fits the costume). Knives and swords are great for short range combat, and if they have a hilt they can block incoming slashes (which was the initial main worry), but by making the whole design thinner and sleeker the weapon itself is able to block attacks, and because every part is dangerous Mitzuki just has to worry about moving it rather than making sure he has the right side and angle in the right spot. As an add on steel tipped toes/elbows/knees could be useful, but require yet more training to make use of (but theyāre easier to keep hidden and could act as useful gear when up against a wall or needing some surprise). Similar situation for items that can run electricity through them to act like a taser, great in theory but pretty difficult to pull off in practice without proper training (and dangerous besides since one bad placed shock could fry an important organ, especially since you never know if a vestigial mutation ties that sport directly to the heart or amplifies the current or something. Not to mention electricity is pretty variable in effectiveness compared to blunt force due to the number of defensive supporting/vestigial mutations that could interact with it).
On the long range side of things Mitzukiās rather limited quirk wise, but every hero's combat capabilities could be improved with a gun or tranq (assuming you can fit them into the outfit design). Luckily some customization is available thanks to the support course and the advice of Snipe, who probably utilizes all manner of ammunition types. Also while guns and tranquilizers are king, other options like slings, nets, and bombs are plenty useful and at least help patch up that weakness.
Moving onto movement Mitzuki actually has tons of options if his quirk works like I think it does! Water enclosed shoes and clothing would allow for quick movement based on how fast heās moving the water (so around 2-3 times faster based on current strength), which is great for speed and sudden dashes of movement in close quarters (especially for getting away from close quarters combat to better utilize his water). More importantly however is the fact that Mitzukiās water is controlled via telekinesis, and since its range is spherical that includes *upwards*. By moving the water in his outfit up, he could get a very rough version of flight, one thatās probably a bit slower and chunkier than standard water assisted movement since itās just hauling him around against gravity, but thatās a small price to pay for flight. Unfortunately all of these water based ideas would need to be combat oriented, at least until he gets a much higher base energy pool, since hydrokinesis takes up so much more energy compared to basic movement.
Now in the defense department things are a bit more standard again, looking like padding, some occasional armor, and pressurized water containers. Pressurized water should be standard for any specialization since it not only provides a good amount of on demand water, but if it can be intentionally released it could give a sudden burst of water that would bash back any would-be attackers, giving Mitzuki more room and water to work with. As for defensively, if it's put into tiny canisters spread out across the body (or larger ones covering weak points or common areas of attack) then physical attacks that crack the canisters would release all that water directly at the attacker. These would have to be pretty sparing of course, since even if made as lightweight as possible the canisters still hold water, which by itself adds a fair bit of weight (though the previous mentions of easy training means Mitzuki might be able to haul stuff around pretty easily after a while).
Looking at utility, options are pretty sparse again. Stealth is best handled by water-assisted movement since itās harder to be quieter than flight, and if thatās unfeasible itās hard to beat some training and simple padding on the shoes/gloves. And of course the previously mentioned array of bombs are a standard but pretty great way of bringing options to the table. Stuff like electricity (or more specifically net bombs made of conductive material an a decent charge in the center), nets, smoke, basic concussive/force, flash/light, gas, and even water (though in that case better to use a solid ball/needle and use water to throw it around). Lots of options, support department knows best, keep in mind people are surprisingly fragile when not beefed to hell and back like Stain, yada yada yada.
Now it didnāt really fit anywhere above but itās worth mentioning electricity seems like a really good option at first, but it really depends on how Mitzukiās quirk works. If itās pulling just water along then itās leaving any impurities like salts and metals behind, making it pure water, which is one of the most inductive/insulating materials in the world (also leaving Mitzuki a little salt rock as he pulls the sweat away). If it keeps any impurities then tons of options for using mixed water come up, such as water stuck in rocks or slurries and the like for extra mass, or potentially stuff similar to bloodbending in Avatar (though that would require VERY precise control to avoid giving someone a stroke or heart attack). But more relevantly if Mitzuki makes sure to salt his water before hand (or even during combat if he keeps some seasoning on hand) then itāll be highly conductive, and would make for a great weapon if charged via an inbuilt taser.
Second little note that didnāt fit easily elsewhere, but since Mitzuki is already sensing stuff with his magnetic field, itās entirely possible he could train himself to recognize other features as well, such as people sneaking around or as a way to see the insides of things without breaking them open. Since itās not something his quirk naturally does it might be pretty difficult, and is very unlikely to become automatic without serious training, but if it IS possible it would be incredibly useful.
