Skill 4 Requirements:
WITH 10+ Tianjiu Star's blade USE Assist Defence Activation OR Skill 3 Slotted
She needs her passive, which requires 5x Glut. Resources, two of which she can make herself due to assist defence to begin with, meaning that you only need to slot 3 Glut. Skills other than Maost this turn (or just 3 if you utilise Lordsguard).
If you are in Railway in a scenario where we don't need to worry about EGO resources for passives, she can gain +5 Tianjiu on round 1 but unless you have a skill 3 in slot for her to activate Deathrite (or if another Mao unit has Skill 3 on turn 2) on the second round, then she still activates properly on turn 3.
She gains +2 Tianjiu Stars Blade per Deathrite that SHE activates herself, up to 5 times for a gain of +10 per turn. She can also gain +5 for each time she activates Assist Defence, meaning that she can gain up to +15 per turn (or +20 if double slotted).
Her skill 4 gives 2 types of deathrite which she can activate 3 times each, which completely fufils her requirement. If activated through assist defence, this skill gives a total of +5 Tianjiu star's blade, unless Deathrite was activated earlier in the turn by other units more than 5 times. (More than 2 times and the skill becomes Tianjiu negative, however she gets 2 activations on her own due to her counter having 2 coins).
This means that every turn or if unlucky every other turn after round 2 (in railway) or round 3 (when starting without any resources) she can use a skill 4 which is positive in Rupture Count, which auto crits due to gaining 20/4 Poise.
Her competition are below:
Hermes' Georg does in fact have a stronger skill 4 but his requirements mean he can't use it as consistently as Mao Faust.
He requires his passive as well, without which he doesn't gain Hermes stacks based on unbreakable coins.
When ran in Railway, (meaning we don't subtract a round off for passive activation) (which also does not matter due to the fact that its more optimal to use defence skill round 1 no matter what) he can gain [0+ (defence), +4, +4, +4, __Clear__.], meaning a max of +4 per round so long as he only has one skill slot, with it being more realistic to gain only +3 (or only +2 but so long as you only get 1 skill 1 in those 3 turns of attack skills it should be fine).
Unfortunately, due to him only being able to gain +4 per turn in the first place, even outside of Railway (no free passive, which again does not matter) (allowed to be double slotted), he is able to get Furioso at round 5 EARLIEST.
Following when he gets 9 Hermes stacks he gains Unlock 3 which is not a real stage as he gets to Unlock stage 3+1 after using Furioso Replica.
Unlock 3+1 allows for gaining 6 Stacks in a single round (5 max if single slotted, which is negligible) meaning that every 3rd round (assuming that you gain a skill 3 every interval between Furioso) he can use Replica again.
Less consistent, extremely count negative for his status effect (as is his kit as a whole), and less predictable as it relies far more on ideal luck to get the 3rd turn rotation for Furioso.
Unlike Yi Sang, this ID is less viable in terms of being "broken" in my eyes due to, largely speaking, the setup time required.
Round 1 can kill at most 1 ally,
Round 2+ can kill 2 per turn (I know you would think it able to target 4 if you double slot but no the max times she can use Tiansha -- Slay the Heavens is 2 per turn no matter what).
She has 9 Allies to kill.
If she kills a nursefather (Rodion, Yi Sang, Outis, Hong Lu) first, then she can target 2 each following round even with one slot.
This means that for peak output of funny, she wants to use 5 consecutive turns of defence skills (if we make the assumption that enemies can't consistently kill allies, or at least specific ones), where she gains the ability to also use an attack skill on round 4 due to lack of backup units (12 sinners brought rule of Railway my hated)
While again, she may be able to outdamage Mao Faust's skill 4, even being able to theoretically do so on her skill 3, she is compensating (something something Ryoshuu's massive sword) for the fact that she has no allies which are still around to help in terms of damage bar Meursault and Gregor neither of which have anything strong enough to be even considered for comparison on this list.
Ryoshuu can use Absolute String Severance about every 3rd turn on average in my experience, which again matches the low end of frequency, and I want to be clear, in my personal ranking, the main thing that keeps Ryoshuu down to the low end of top 5 is the fact that she requires 9 specific allies and 5 rounds of setup before rocking.
Even without maximum potential, she still performs really well and hence is why is is probably 4th or 3rd on my ranking.
Middle Nursefather Outis:
Earliest you can get Laevatinn is round 4 HOWEVER this relies on an enemy which is able to stagger her round 1.
Also see previous statement about how I think Ryoshuu is slightly worse because she relies on having specific units or allies to give her full potential.
Knight of Despair Rodion:
Yeah I can get behind her (something something joke about getting behind Rodion? I'm being too autistic about optimisation to pretend to be horny properly) being up there. She is without doubt at least top 10, and is single handedly the best Sinking unit in general, although she is more reliant on her status effect to carry her in lieu of raw damage output when compared to an ID that can do both to extreme degrees (MAO FAUST).
Copy Paste this exact paragraph for Fauvist Rodion but replace sinking with Bleed.
Thumb nursefather Rodion:
Earliest Disposal is turn 4, requires at least 6 turns of cooldown between first Disposal activation and the next overheat timer.
Unlike others, even when single slotted she doesn't only have the 6 round (non forced) average for skill 3s, due to cloning her skill 4 on kill, which doesn't work in most boss fights however.
