Marie Ijiyuuin is the older sister to Serena in their vampire family. She possesses blonde hair and blue eyes. Despite Yuuto's presence being intended as sacrificial atonement for his father's transgressions against the family, Marie openly pursues him, fully aware of his designated fate. She rejects the family patriarch's unyielding grudge against Yuuto's father, whom the elder views as a traitor, directly challenging this perspective by criticizing the patriarch's prolonged isolation from the world. Marie exhibits no shame regarding her desires and possesses strong determination, relentlessly pursuing any course of action she decides upon.

Her investigation into Yuuto is significant. Intrigued by his unique ability to survive Serena's typically fatal energy-draining abilities, Marie develops a personal theory to explain his resilience. She persists with her inquiries despite facing the patriarch's strong opposition and denial of her hypothesis. This pursuit involves her personal investigation into Yuuto's circumstances, during which she develops a fervent attraction to him. She pursues this romantic and physical interest with fiery assertiveness.