Like his two younger brothers, he lived next door to the heroine since they were children. He rarely interacted with her, due to her spending more time with his youngest brother Toma than him. When his brothers formed a musical group, he became the lead singer.
Despite being her adoptive brother, he's violently possessive of Hatsuka. He buys her a necklace, which he believes will mark her as his. When he walks in on his brother Toma who had fallen on top of her, Shion pulls him off and demands to know what he was doing. He even imprisons her by chaining her to a bed to keep her from leaving and from anyone trying to take her away from him. When she tries to escape in his Extreme Love End, he strangles her in a last-ditch attempt to prevent her from leaving. In his Crazed Love End, it's revealed that he had been taking pictures of Hazuki since they were little and had kept them in an album.