I had some fun ideas for how Simon and Grace could be from the same universe and thought I would share.
WARNING: COMPLETELY INCORRECT SCIENCE AND KIND OF INCORRECT TIMELINES AHEAD
(I have seen both movies and read Project Hail Mary. HOWEVER, I watched Iron Lung the day it came out and I don’t remember specifics. If something is completely wrong/implausible PLEASE let me know.)
Ryland Grace: Age 32 at time of coma (43 earth years when he wakes up)
Simon is not a Homo Saipan, though he and Grace share a far more recent common ancestor than Humans and Astrophage (game theory time, a multicellular eukaryote got rocketed at near light speed during the Cambrian extinction and managed to somehow survive for 300+ years until the thing it was living on got sucked into an orbit). For unknown reasons (aka I made it the fuck up), the Mira star system gives off an exceptional amount of Infrared light, and said IR light and its resulting radiation causes rapid evolution. This is how Simon's branch of Hominids became so close to resembling true humans so quickly. One key difference though is that these new hominids can see in infrared (we will get to why that’s important)
Can see in infrared and regular human spectrum
Lifespan: 40-50 years (can be elongated with modern meds)
Retained several internal structures similar to bony fish ancestors, though they are redundant (like appendix) in modern times. Likely due to rapid evolution.
Significantly stronger physically, with denser bones (why Simon can do what he does lol)
Can withstand more IR radiation than normal humans (with limits)
More layers of skin (can be shed when apoptosis fails to prevent surface skin cancer)
Rapid regeneration (compared to humans anyway)
Due to similar conditions to earth, societal development occurred in a very parallel manor, though much more rapidly.
Circadian rhythm lasts 48 hours (sleeps for 12, awake for 36) (not based on a day-night cycle, as they lacked one. Instead, body detects when energy becomes <25% and they immediately crash for around 12 hours. Similar to instantaneous REM of narcolepsy.)
Stores much more energy than average human (explains why he doesn’t look underweight after being kept in not great prison for 16 years)
Skipping ahead, the blood ocean is not made of blood. Rather, it is a mass amount of astrophage that escaped into the heat of the ocean after the death of the Mira stars. Considering they are parasitic in nature, astrophage can detect the end of its hosts energy. In order to survive and hopefully find a new host, they store the energy they have as much as possible and seek out the next hottest object near them with a carbon dioxide atmosphere. In this case, the oceans on AT-5 and the other three moons were habitable for them. Mass amounts of astrophage spawned from the death of the Mira stars, and they are now all clustered in these waters. The red coloration comes from Homo Stellamirus’ ability to see in infrared. Just like the Pretrova line, astrophage is producing infrared to move around (though much less due to trying to save energy.). The need for the X-Ray camera came about as their normal cameras include infrared light. The astrophage also creates the blood-like viscosity of the ocean.
The “eel” comes from the first explorers the Consolidation of Iron sent into the ocean. Their submarine was not airtight, and combusted. Instead of immediate death however, the intense amount of infrared radiation in the water caused instantaneous mutative adaptations. In short, the bony fish structures evolved in a matter of a few seconds in order to survive in the blood ocean. The people involved were all somewhat melted and grafted into one being with several consciousnesses.
The voices Simon heard, as well as the god he saw were all hallucinations from stress, isolation, X-ray radiation, and increasing IR radiation. His mutations are a scaled down version of the ones sustained by the eel. As they come from the rapid mutation of his own gene sequences, they are relatively harmless, if a bit painful.
The Mira star system is closer to 40-Eridani (this might be a blatant lie, I can’t really find concrete info on their locations so I have no idea lol) so scientists were able to notice a change in it far more recently. After Rocky’s team left, they sent another team to go examine the dead stars. During this, Simon was discovered barely clinging to life. He was exceedingly lucky, as he avoided falling into the ocean (after Ellie chomped the iron lung and his arm in one bite) and was found unconscious on a large plate of metal from the SM-13. Simon was rescued and returned to Erid around 6 months before Grace and Rocky returned. During these months, he was looked after by Adrian, who needed a distraction from Rocky’s absence. They learned how to communicate via sign language, though Adrian can now understand his words (he speaks and signs simultaneously)
Born 348 EIC on “Mars” (was the planet relative to his “earth”, after learning English he was forbade from his original language and therefore he remembers the planets in English terms)
Was 9 during the Quiet Rapture
Was 14 for Filament Station (child solider)
Growing up in Eden, he was selected at the age of 10 to learn to pilot and maintain their space vehicles, until he was taken from this role to be used in the war (His knowledge of rudimentary engineering was apart of why he was so successful as ‘The Butcher’, as he made traps and unique weapons).
Spent 16 years in the custody of the COI: Now is 30
His basic piloting skills were honed and then used by the COI to train others. As of 378, enough people have been sufficiently trained that they now consider Simon to be of no more use. This is why they allowed him to volunteer for Conviction Realization.
Mutations/appearance: Left eye is red and sees exclusively in infrared. Sharp teeth protrude from extended mouth on left side of face, starting from corner of mouth to cheekbone. Fin like left ear ( similar anatomically to a bats wing). Gills on either side of neck (capable of breathing underwater). Missing left arm (during his radiation-induced hallucinations, Ellie bit his arm and he had to pull what remained of it out of her jaws. This was somewhat fortunate though, as without it he was unbalanced and fell unconscious backwards onto the metal paneling he was rescued from.)
Still has minor visual and auditory hallucinations from residual radiation damage. (Like the animals in Chernobyl, the radiation is self contained and harmless to him (physically) and others)
Speaks English as a result of Eden intercepting audio from earth satellites (they mistook it as verbal guidance from the tree and required everyone to understand it) (Alternate reality in which Voyager 1 had recordings to teach aliens english and got absolutely yeeted into deep space)
There’s something out there in space that really likes to send things at the Cetus constellation at near light speed (Black hole misinformation go brr)