Subnautica mercreature AU where Eddie is a reaper leviathan and Volt is a ghost leviathan
the colors, sizes, and demeanors are all so them
Eddie, being a reaper that stays in the volcanic regions of the world, discovers Volt, a ghost leviathan that had been ousted from its group as a juvenile/ is a loner that doesn't remember where it came from. Ofc they fight at first; they are both large, highly aggressive creatures that attack on sight, and Eddie feels his territory is being threatened. Volt overpowers Eddie, naturally being stronger and bigger, but when Volt doesn't kill Eddie, he's shocked, reluctantly appreciative, and lets Volt stay in his territory.
LW being the lone survivor from the Alterra crash and discovering these giant mercreature men when they're just trying to cure themselves of this alien disease. Eddie and Volt would stalk LW at first, intrigued by this small foreign creature and the machines they had with them, but when they would get too close to their nest, they attack them and their vehicles.
Eventually, LW builds a base in this region, not needing to go to the surface much anymore, and is cornered by the two mercreatures that had been after them for months. Instead of killing them, Eddie and Volt tease and interrogate them. LW shakily and desperately explains all the events of the game up until that point, and Eddie and Volt are hesitant to trust them, but have no reason not to. All three of them know LW could be killed and forgotten easily, like the rest of their crew.
LW is still determined to get off the planet, investigating the secrets and the ones who came before, but Eddie and Volt deter their research at every turn. It gets to a point where LW yells at them and shuts themself in their Cyclops, going back to the safe shallows, to where Eddie and Volt can't follow. They were lucky to escape; their Cyclops almost failed several times, and they attracted the attention of several other creatures during this fight, but LW made it. They have a lot to think about now that they're on the surface and by themselves again.
You can decide what your LW does! Does your LW remain on the alien planet with their mercreature partners, or do they return to their old life on Earth as an Alterra Researcher? Personally, I'm curing the world and staying on it with them because I'm not leaving two hot monster mercreature bfs, ya know?