Remi, with Kuroma.

Kuroma (クロマ) is the anthropomorphic note that follows Remi Otogiri in Groove On Fight. It is a demon that was created by her mother to be her bodyguard and is usually sealed in Remi's brooch.

Kuroma appears constantly with Remi in battle and is utilized as something of a weapon. It has the ability to metamorph, usually in the form of a blade weapon, which it will use to attack opponents with devastating results.