Kuro Kiyosumi is an idol belonging to 315 Production and a member of the unit Sai. He comes from the distinguished Kiyosumi family, which is renowned for its tea ceremony tradition, and prior to becoming an idol he served as a tea ceremony master himself. This upbringing left him with a deeply formal, reserved, and stoic demeanor. He often carries himself with the gravity and propriety of someone much older, and while he is polite and well-mannered in structured or ceremonial settings, casual social situations make him visibly uncomfortable and uncertain. His sheltered background means he sometimes struggles to grasp everyday informality, and he can come across as overly serious or unaccommodating.

Within the short-form anime The Idolm@ster SideM Wake Atte Mini!, Kuro appears alongside the rest of the 315 Production idols in chibi-styled comedic vignettes. His role highlights the contrast between his rigid traditional sensibilities and the more relaxed, often chaotic environment of idol life. Though he is earnest and diligent, his attempts to navigate offstage camaraderie frequently lead to endearing awkwardness. He shares his unit with Kirio Nekoyanagi and Shoma Hanamura, and these relationships gently push him toward a broader understanding of social interaction outside his ceremonial expertise.

Kuro's primary motivation is to grow beyond the confines of his past. Becoming an idol represents a deliberate step into a world that demands flexibility and emotional expression he is not naturally inclined toward. Over time, his experiences with his unit and the larger agency slowly chip away at his rigidity, encouraging small but meaningful personal development. His most notable ability is his profound mastery of tea ceremony, an art that demands precision, patience, and aesthetic sensitivity. This skill occasionally surfaces in his idol work and highlights his refined, disciplined nature, even as he learns that not every situation can be approached like a formal tea gathering.