Makabe Shizuru grew up in a single-parent household, and was left alone after her mother was killed in a traffic accident. However, on the night after the funeral, a man claiming to be his father appeared and offered to take Shizuru in. And so, when he visited the man's house, he found Hasumi Shion, a popular female student at the same high school, waiting for him there with a cold gaze. ‘Well, I'm proof of her father’s betrayal. That reaction is expected…’ Nevertheless, they were still siblings and were going to live together under one roof. On the other hand, Shizuru has long been pursued by a beautiful, refined lady, Takinami Ruika, a senior student at his school. A cold half-sibling and a refined lady(?) Shizuru, who was supposed to lead a quiet school life as the only member of the library committee, but one day, his surroundings became rowdy and colorful.