Lumi is the player character and main protagonist of the Cats are Liquid games. She is a white cat with a blue face. In A Better Place, Lumi's facial expression changes based on how many lives she has. In A Light in the Shadows, she is shown to glow rather brightly. She is normally depicted as smiling, though she rarely seems to be truly happy.

Lumi is the main protagonist in all current Cats Are Liquid games. In both games, her actions and thoughts are narrated until the final level.