Flat is a Supporting Character in Onegai My Melody. He is a blue mouse with yellow ears who wears an orange or pink ribbon on his tail. He is the closest among My Melody's animal friends. Whenever there's trouble, especially a curse created by Kuromi's magic, My Melody sometimes casts a spell on Flat to deal with it. There have also been hints that Flat may have a crush on My Melody; for example, blushing when she hugs him in one episode.

Flat also has great social skills when it comes to interacting with the opposite gender. With these, he occasionally gives pointers to Kakeru when trying to contact Uta in certain situations.