Misonou Kai is the younger fraternal twin brother of Hamura Shou. Separated during childhood after their parents' death, both entered an orphanage before Kai was adopted by the wealthy Misonou family, controllers of the Misonou Combine. Due to Shou's earlier instruction to forget him, Kai developed amnesia regarding his twin and their shared past, leading him to initially deny their relation upon reuniting at Yuusei Academy. He carries the title of prince from the Winfield kingdom, a status marked by his manifestation of white wings symbolizing royal heritage.

An honors student excelling academically, Kai transferred to Yuusei Academy. His personality is kuudere—outwardly cold, mature, and stoic, with a sharp, cautious approach, yet he harbors a softer interior especially toward those close to him. He maintains a long-standing relationship with his childhood friend and protector Nagi Uesugi, whom he met after his separation from Shou. This bond becomes central when Nagi is seemingly killed during an attack by the black-winged faction, triggering Kai's berserk state until Shou intervenes. Nagi later resurfaces with amnesia.

Kai's family faces manipulation by Ran Sakakibara, a retainer and lover of the black-winged commander Reiya Wakabayashi, explaining Kai's prior awareness of Ran. Forced to act as a "puppet" under the black-winged faction's control, Kai experiences significant internal conflict. Physically, he possesses long blonde hair past his hips, green eyes, and stands 167 cm tall. He is often mistaken as the older twin despite Shou's actual seniority and typically wears a school uniform.

In the spin-off *Kuro no Zanei*, Kai's daily life at Yuusei Academy is explored, highlighting his academic role as representative chairman and his cautious, preventative approach to problems. His background includes a gentle childhood demeanor contrasting his reserved teen self. Kai dislikes junk food and shares a March 7 birthday with Shou.