Ginpei Moroboshi, often called Gin-chan by those close to him, serves as the chief manager for the band Black Stones, also known as Blast. First appearing in the story at the age of twenty-eight, he is an employee of Gaia Records and plays a crucial behind-the-scenes role in the band's operations. Physically, Ginpei stands out among the typically slender characters of the series due to his stocky, muscular, and rugged build. He has a buzz cut, thick eyebrows, brown eyes, and a thin pencil mustache. He also has pierced ears and is often seen wearing small hoop earrings, and his fashion sense is generally casual and sporty with a hint of flashiness.

Ginpei possesses a very distinctive and flamboyant personality. He is openly gay and speaks in onee-kotoba, a feminine or effeminate style of speech in Japanese, which gives his conversations a unique and memorable quality. He is easily excitable and has a sassy, teasing nature, but this exterior belies a diligent, competent, and deeply caring individual.

His primary motivation is the success and well-being of Black Stones, and he works tirelessly as the true powerhouse behind the band. He looks out for the group more than anyone else, always putting their interests first and acting as a reliable, unsung hero. While he is often playfully mean to the lead vocalist Nana Osaki, whacking her on the head or quarreling over trivial matters, it is evident that he genuinely cares for her. One of his most notable traits is his open crush on the band's drummer, Yasushi Takagi, whom he often calls his favorite. Ginpei treats Yasu noticeably nicer than the others, reportedly because he admires his bald head, and he has expressed jealousy over Yasu's relationship with Miu Shinoda. In contrast, he is remarkably indulgent and kind toward the youngest member of the band, Shinichi Okazaki, showing him extra kindness and being unwilling to scold him harshly.

Within the story, Ginpei acts as the dramatic manager for Blast, handling their professional affairs and guiding their career. As the narrative progresses, his dedication never wavers, cementing his role as a vital and unforgettable part of the group's world. His development is subtle, primarily shown through the deepening of his loyalty and his growing importance as a pillar of support for each member during difficult times. His notable abilities include his sharp management skills, his physical strength, and his unique talent for lifting the group's spirits with his exuberant and unfiltered personality.