Keiichi Hiiragi, a senior at Yumegaoka High School, balances his identity as a gifted violinist and celebrated teen heartthrob with a clandestine role fueling dark forces. Initially portrayed as an antagonist, his violin performances channel Dark Power into Kuromi’s Melody Key, aiding her quest to resurrect the Spirit of Dark Power. Driven by boredom and a thirst for hidden influence, he collaborates with Kuromi while maintaining an aloof public persona, secretly navigating alliances and rivalries behind the scenes.

Consequences from his crimes against Mary Land later force him into a reluctant redemption. Coerced under threat of punishment, he covertly assists My Melody and Uta, transformed by magic into Usamimi Kamen—a rabbit-eared superhero persona clashing with his apathetic nature. Though he resents the role’s cheerful facade, he begrudgingly atones for his past, torn between disdain and duty.

His privileged upbringing includes a contentious bond with younger brother Jun, who inherits Keiichi’s former role as Kuromi’s Dark Power source. Their rivalry simmers with Jun’s provocations and Keiichi’s volatile reactions, while the family’s devoted butler, Sebastian, underscores their affluent life.

Romantic entanglements entwine him with Uta, who harbors unspoken feelings, and Kuromi, whose obsessive fixation on him overrides her ambitions. His interactions with both remain enigmatic, though a fleeting attraction surfaces toward Kuromi’s temporary human form, Kurumi Nui.

Evolving from self-serving antagonist to a grudging ally against darkness, Keiichi treads a tightrope between resentment and responsibility. His mother’s affectionate nickname “Kei-kun” whispers of familial warmth buried beneath his detached exterior, hinting at layers unseen in his brooding journey.