The strongest hitman of the Niounomiya Troupe. He is the split personality and older brother of Rizumu Niounomiya. Though he identifies as a male, his actual body is that of a female due to him being a split personality.

Spoiler

In reality, Izumu is his very own person, rather than a split personality. He is typically near his younger sister, Rizumu Niounomiya, though he stays out of sight, only coming out when necessary. Like other Niounomiya, he is the product of a lab experiment to make the strongest killer. Izumu is pure strength without weakness, contrasting Rizumu's pure weakness without strength.