Among U: Red Imposter flips the usual space-crew game around and puts you in the role of the impostor. You are the red character on board a spaceship full of white crewmates, and your mission is to take them out one by one without getting caught.
Each of the 24 levels is a section of the spaceship with crewmates going about their tasks. They are trying to complete missions that will expose you and throw you off the ship, so you have to act first. Sneak up on crewmates when nobody else is watching and eliminate them quietly. If another crewmate spots you, the plan falls apart. Clear every crewmate on the level to move on.