Mokusei is a Musicart embodying the composition "Jupiter, the Bringer of Jollity" from Gustav Holst's orchestral suite "The Planets" Op. 32-4. Her official designation directly references this musical source. She makes a brief, non-speaking appearance solely in Episode 12 of the anime series. The narrative provides no details on her background, origins, specific abilities, relationships, character development, or participation in events beyond this single episode. Her presence remains exclusively within this supporting role across all documented official media.