A famous violinst and teen heartthrob, Hiiragi's violin playing supplies Kuromi's Melody Key with Dark Power in the first series being the apparent chosen of the Melody Bow. Very popular around girls he is often secretly agitated or indifferent to ladies. He joins Kuromi's side to unleash the Dark Power seemingly out of boredom but soon is the de facto leader of Kuromi's group. He is not above subterfuge to further his goals and keep the knowledge he is working with My Melody's enemies a secret from the heroes though he interacts with them freely. In ~Kurukuru Shuffle!~, he transforms into Usamimi Kamen with My Melody's magic. Forced to become My Melo's super hero due to his actions in the first season, he absolutely hates becoming Usamimi Kamen(a humen shape of my melo), as he is often apathetic and unenergetic when My Melo summons him.
His mother calls him Kei-Kun.