@-marshhmallow- How about that: They all once used to live on a planet together. All of the small among us colors, but someone destroyed the planet somehow or made a toxic gas spread all over the planet. They had to think fast so they flew away in spaceships. Somehow the one who destroyed the planet/made the gas spread got into the ship too though, without them knowing at first. But somehow they find out. No one trusts the other anymore from that point on and it's on them to find out who it was though. (Something like that, woops^^")