Kai Kusano

Kai Kusano is the older brother of the female lead, Shizuku, with a ten-year age gap between them. His dedication to mountaineering and bouldering has shaped his athletic build, giving him a bright and approachable presence. Known for his near-obsessive protectiveness over his sister, he frequently shows up out of concern for her well-being. He also serves as a senior colleague to Yui Hoshizaki in the workplace and harbors feelings for her. Throughout the story, Kai acts as a warm, supportive figure who bridges the relationships among the characters while keeping a watchful eye on his beloved sister.