Kosuke (コースケ) is Takashi's brother and friends with Makoto and Miu. He taught Makoto how to play the game along with Takashi. When he sees Miu upset that she hasn't seen her brother in a long time, Masquerade tells him if he can defeat the Battle Brawlers, he will reunite Miu with her brother. He brawls Runo and Marucho alongside Takashi but relinquishes the Doom Card when Miu starts crying. They then play them again and lose, though they were glad they had fun. Miu then gives them both a kiss on the cheek for trying to help her. He brawls with Darkus Bakugan.