Rouge

ルージュ

Rouge descends from the sky like an angel, landing directly on top of Yusuke; however, she suffers from amnesia. The only thing she remembers is her name. Yusuke provides her with a safe place to stay while she tries to recover her lost memories. Meanwhile, she begins to develop feelings for the high school student. She does her best to repay his kindness by cooking meals for him, doing household chores, and assisting with shopping.
At one point, she is kidnapped by a demon-like woman named Vega. Yusuke and Rouge’s two sisters, Kaiga and Meiga, set out to rescue her. They encounter Vega, who transports the three of them to the Underworld. There, Rouge is trapped inside a magical sphere while her friends attempt to save her. It is revealed at this stage that Rouge is the Princess of the Underworld. Eventually, Vega attempts to kill Yusuke. Rouge’s emotions surge within her, and she unleashes a hidden power to save him. This demonstrates that she indeed has some connection with Kaiga and Meiga, lending credibility to the theory that she is the Princess of the Underworld.
The four continue to live together until the day she can recover her past, with her bond with Yusuke only strengthening.