The older brother of the twin unit Twinkle Bell. With his my-pace, leisurely personality, Mutsuki is the exact opposite of his lively brother Satsuki Kururugi. He loves sleeping so much, he'll even doze off in the middle of his conversations.

Mutsuki tends to go along with Satsuki's pranks relatively openly, but he's also a helpful older brother who will properly put a stop to pranks that escalate too far.

(Source: Etoile Stage Wiki)