Chibimoth

Chibimoth is a secondary character in Rewrite, and is Kotori's pet. He appears near the end of the Common Route and has a reccuring role in Kotori's route. Although Kotori claims he is a dog, Kotarou and many other characters frequently comment that he looks nothing like a normal dog. Chibimoth has exceptional strength and speed, despite his small stature. His catchphrase is "Mosu! Mosu!" and he uses it regularly.

(Source: Rewrite Wiki)