#disp

First, Robert isn’t immortal. He dies and dies often, but comes back to life. Meaning that he is just incapable of staying dead #cockroach

The mechanics of Robert’s inability to die is due to three major processes:

Ability for cells to continue functioning while the heart is stopped.

Ability to restart the heart without external stimulation.

Ability to heal damage that caused death via increased activity in processes involving programmed cell death, wound healing, tissue regeneration, stem cell generation and differentiation.

Before we get started, there’s a lot of nuance needed to understand the differences between the clinical/legal definition of death and the scientific process of dying. Legally, someone is considered dead when their heart and lungs stop and are unable to start again, some places also will also consider someone dead if there is no activity in the brain and brainstem without any chance of activity coming back.

Typically when we hear that someone died, we assume when someone dies, their entire body turns “off”. And while that is true in the sense that part of the body has turned off and will never turn back on (i.e. heart, lungs, brain), the rest of the body is still alive. This is why we can do organ transplants. So now we know death is a process, and that while someone’s heart may have stopped and they will not come back to life, their cells will still continue to work. 

Problem 1: Cells can’t live without energy, and can’t make energy without oxygen

The main reason why the body’s cells start to die is because the lungs are no longer exchanging carbon dioxide (CO2) with oxygen (O2), and the heart is no longer pumping blood to push nutrients to cells and take away waste. The inability to make energy combined with the build up of waste leads to cell death.

Getting oxygen and removing CO2 is important because our cells use oxygen to turn glucose into ATP, which is like the cell equivalent of gas for a car. When cells use oxygen to make energy, it's called aerobic cellular respiration, and the oxygen makes this process super efficient. There's this whole process that converts glucose into like 2 ATP and a shit ton of protons. Then at the last step, there's a process called the electric transport chain that uses the protons to make ATP. The cool part is that it's not protons turning into ATP, but instead it's this enzyme (ATP synthase) that's built like a tiny molecular wind turbine. It uses the rushing of protons through the enzyme to push the “propellers” and use the resulting mechanical energy to convert ADP into ATP.

The thing is that something needs to keep luring protons across the enzyme, which is where oxygen steps in. In order to have protons rushing continuously, oxygen combines with the protons that rush through the ATP synthase and this combination creates water. This happens on the side that protons are rushing into, essentially clearing up the end of a conveyor belt to avoid backups.

So when cells don’t have oxygen, they can't use the above system, so they use anaerobic cellular respiration to convert glucose into ATP. Anaerobic respiration is a normal process, but it’s highly inefficient, so the human body can’t rely on it to survive. For reference, aerobic respiration converts one glucose to 30-38 ATP, while aerobic respiration converts one glucose to 2 ATP. Anaerobic respiration also produces byproducts like lactic acid, which is why your muscles burn during an intense workout, because your cells are using anaerobic respiration to supplement aerobic respiration.

Without ATP the cell can’t do what it needs to do to survive and then it dies. Because of this, high energy cells that require lots of oxygen to survive (ie neurons in the brain) die first, this is why when someone goes into cardiac arrest, it's important to start CPR immediately to prevent brain damage. 

Problem 1 solution: Get energy without oxygen using a backup energy generation pathway

So given all of this, Robert’s body needs a way to keep cells alive in the time between Robert’s death and recovery. This means the cells need a way to obtain energy while the heart is unable to push fresh nutrients to them. To achieve this, I think Robert’s body would have adapted to have a more efficient way to do anaerobic respiration to keep more of his cells alive when his heart stops beating. My main hypothesis is that his body accepts sulfur compounds (which are naturally ingested through nuts, beans, eggs, etc) as an alternative to oxygen for a terminal electron acceptor. Although less efficient, sulfur can accept protons to turn into hydrogen sulfide (H2S). 

The byproduct, H2S, is fine at low concentrations, but super toxic at high concentrations. This toxicity will cause cell damage, which pushes cells to release a bunch of chemicals in response, one of those things being reactive oxygen species (ROS). To handle H₂S exposure, Robert’s body would need naturally elevated vitamin B12 (hydroxocobalamin), which binds to sulfide and reduces serum H₂S concentrations. This is actually an experimental treatment for hydrogen sulfide poisoning. Bonus side effect: This adaptation would make him functionally immune to cyanide poisoning, since the same compound treats cyanide exposure.

This sulfur-based system runs at a low level even when Robert’s alive, but ramps up dramatically when he dies. I’ll get into some of the side effects of this later.

Problem 2: Getting the body to be… not dead

Problem 1 shows us how important the heart is for mitigating the amount of damage Robert’s body obtains between death and resuscitation. So the first priority is getting the heart to start again.

Unless the heart breaks open, the heart typically stops beating due to an electrical signaling issue. This is why someone on a pacemaker may appear alive on a heart monitor even if they’re dead (the heartbeat “lub dub” will still sound as if they’re alive). The pacemaker mimics the job of pacemaker cells, which are in the sinoatrial (SA) node. Unlike the battery in a pacemaker, pacemaker cells rely on a flux of calcium ions (Ca+) to trigger an electrical charge, which causes the atria to contract (first noise “lub” in the heart beat) and moves down the electrical pathway and eventually causes the ventricle to contract (second noise “dub” in the heartbeat). So essentially, we need Ca+ to cause that first electrical impulse. Fun fact: adenosine, a drug we give when the heart is beating dangerously fast, temporarily stops the heart from beating by binding to Ca+. This momentary pause resets the rhythm, which is super cool (and scary lol)

Problem 2 solution: Induce the heart to restart by breaking open cellular calcium ion reserves

Okay so now we know that we need Ca+ to get the heart to start beating. Well remember the ROS that formed because of high H2S? Well ROS can break down the lipid bilayer, which is what the cell membrane and vesicles are made of. So Robert’s cells actually have an increased number of lysosome associated membrane proteins to protect themselves from being completely destroyed by ROSs. But there's one set of vesicles that don’t have this protective barrier, vesicles containing Ca+. The vesicle breaks and Ca+ enters the extracellular space, and when that happens near the pacemaker cells, we could hypothetically get the heart to start beating.

So at this point when Robert’s heart stops, the following happens: Heart stops → cells realize they aren’t getting oxygen and switch to sulfur based anaerobic respiration → H2S forms, damaging cells → damaged cells release ROS in response → ROS breaks down unprotected lipid membranes → Ca+ vesicles break open → flux of Ca+ causes pacemaker cells to emit an electrical charge → heart begins to beat again.

Problem 3: Expedite healing without accidentally getting cancer

This one is a given. Restarting the heart is useless if the reason it stopped isn’t fixed. So instead of talking about why injuries are bad, I’ll explain how his mother’s powers worked so we can understand how Robert’s differs

Robert’s mother had a mild healing power. Her healing did not have an activation requirement, and essentially was a more efficient version of human healing using the enzyme pathways below.

Plasmin & Alpha-enolase: Crucial for skeletal muscle repair and regeneration.

PKM2 (Pyruvate Kinase M2): Key for connecting inflammation to cell proliferation during wound healing.

Mst3b (Mammalian Sterile 20-like kinase-3b): Promotes nerve fiber (axon) regeneration in the nervous system.

Beta-secretase 1 (BACE1): Involved in nerve regeneration, though sometimes acts as a negative regulator.

Cyclooxygenases/Lipoxygenases: Involved in nerve repair.

Proteolytic Enzymes: Break down scar tissue, allowing for tissue replacement. 

Since Robert doesn’t know anything about her, the nature of her powers likely won’t be in the fic. So I’ll add here that because these enzymes are upregulated, Robert’s mother likely had glass skin without any scarring. Robbie saw this and assumed that she could heal from anything, and therefore be immune to death. He was wrong. Her body could only heal what it thought was broken. This means that aging was something the body saw as normal, so she aged like normal, and would likely die of old age. Unfortunately, the enzymes above are also the same ones that are upregulated in cancer, so having these enzymes upregulated without an upregulated system to clear out damaged cells means that she would have likely developed cancer before she could die of old age. For the record, I am not giving Robert cancer, some of the adaptations between him and his mother (listed below) addressed this cancer risk.

Problem 3 solution: The phoenix effect via Caspase-3

Since Robert’s mom had a baseline higher healing rate, which increased the risk of cancer, Robert’s powers changed the healing activation requirements to protect him from the cancer risk. This is achieved via activation of inflammatory pathways, specifically caspase-3.

Caspase-3 works paradoxically, it triggers both cell death (burning away) and cell regeneration (rebirth) through a process called apoptosis-induced compensatory proliferation (AICP). It’s involved in tissue regeneration, wound healing, and stem cell generation.

When Robert dies, the H2S and ROS levels rise and induce an inflammatory response that sparks a massive caspase response when his heart restarts. But instead of just killing old/dying cells like normal, his caspase system targets ALL damaged tissue and triggers aggressive stem cell generation and differentiation to repair damaged organs. At this point, the healing factors his mother had kicks in to heal the body.

This is why he still scars, because he’s not regenerating from “nothing” back to “perfect.” Instead, he’s going from dead, to damaged but alive, then healing at a rapid rate from there. His body is essentially doing extreme emergency triage and repair, not a total reset to factory settings.

Power drawbacks:

Obviously aside from the fact that Robert doesn’t want to be alive, this power has some drawbacks

Chronic pain: Every time Robert dies, a lot of his cells either die or are under massive stress. This releases purines (components of DNA/RNA), which break down into uric acid.

Chronic elevated uric acid causes:

Gout-like symptoms - crystallized uric acid deposits in joints

Joint pain that gets worse throughout the day (explaining why his joints ache by noon)

Potential kidney stress from constant filtering

Inflammation in tissues where uric acid crystallizes

If he died less frequently, his body could process and clear uric acid normally through his kidneys. But the constant death-regeneration cycle means he’s always dealing with elevated levels. 

Chronic low energy: Robert’s body has massive resource requirements for regeneration.

During normal healing (no deaths):

His body heals like the typical normie

Resource needs are elevated as his body tries to stabilize post reset

During death-regeneration cycles:

Sulfur-based respiration needs MORE glucose to produce the SAME amount of ATP that oxygen would (remember: way less efficient)

Massive stem cell generation requires proteins, fats, minerals

Tissue reconstruction demands raw materials his diet can’t provide

This puts him at high risk of cachexia, which is a wasting condition where the body consumes more energy and resources than it has available.

Cachexia symptoms Robert shows (especially as deaths become more frequent):

Wasting muscle mass (his body cannibalizes muscle for protein)

Weaker, more brittle bones (calcium and phosphate redirected to more critical repairs)

Chronic fatigue (never enough ATP for normal function)

That feeling of being “off-kilter” and shaky (metabolic dysfunction)

Rotten blood: As we’ve established, Robert’s death causing an increased concentration of H2S and ROS in the body. Hydrogen peroxide is a form of ROS, and idk if yall ever tasted that, but it is GROSS. This is why Sonar and Coupé thought his blood tasted rancid. It’s literally full of hydrogen sulfide (which smells/tastes like rotten eggs) and ROS (which has a bitter metallic taste), especially right after a reset. The taste/smell is strongest immediately after death and fades over time as his body processes it out. It likely also burned their mouths a bit, since both H2S and ROS are a mucosal irritant. Also, chronic nutritional deficiencies will leave his tissue tough, gamey, and bitter (think of why wagyu is so good, its because fat is marbled across the muscle fibers).

The Phoenix Paradox

So to summarize the costs so far: Robert’s blood tastes rancid, his joints ache, he’s chronically fatigued, and his body is slowly cannibalizing itself. But I think the worst of all is that he has no fucking idea. He’s never been to a doctor, and his self-sacrificing ass will never let him but himself first in any scenario.

As I say in the fic summary, every power has a price. Robert’s is that his body is simultaneously his greatest asset and actively consuming itself, turning into the final paradox. Dying heals his injuries, but dying less often would actually be healthier for Robert long term.

Unfortunately, Robert’s stuck in a brutal feedback loop:

He dies frequently (intentionally or in hero work)

Frequent deaths → chronic H₂S poisoning + uric acid buildup + cachexia

These symptoms create the “static under his skin,” joint pain, fatigue

These sensations feel wrong, like something needs to be fixed

He thinks dying will reset/fix it

Dying temporarily relieves some symptoms but perpetuates the underlying problems

Return to step 1

If he could go longer between deaths, his normal healing factor would handle day-to-day damage, his body could clear toxins, and he could actually maintain his muscle mass and bone density. But he’s been conditioned by years of thinking frequent death is necessary.

If he’s malnourished, doesn’t have enough resources, or the damage is too extensive, healing is incomplete. He might need multiple deaths to fully recover, or end up with permanent damage if conditions aren’t right.

Robert inherited and metabolically amplified his mother’s healing factor through the caspase mechanism, but it’s still constrained by biological reality. You can’t build tissue from nothing.

This is why he had lasting damage even after his post coma reset. The explosion, coma, malnourishment, body running on fumes, he simply didn’t have the raw materials to complete repairs. The twinkies diet isn’t cutting it when his body needs the caloric and nutritional equivalent of an Olympic athlete during training.

If you’ve made it this far, thank you for indulging my biochemist brain. Every power has a price, and I wanted Robert’s to feel like it came from something real, even if that ‘something real’ is running on H₂S fumes and spite.

References

A lot of this was off the dome, but heres some specific papers I read through. Happy to provide others if people are interested!

Paper about caspases

Paper about metabolites that form during death

Paper about sulfur compounds replacing oxygen