Yusuke Mizuki is an orphan living independently while attending high school, managing his own residence amid frequent tardiness to classes, reflecting an unstructured lifestyle. Financially self-reliant, he struggles consistently with rent payments. His life shifts dramatically when Rouge, an amnesiac princess from another dimension, falls from the sky onto him. Reacting with practical compassion, he prioritizes her care by having his female landlady assist with undressing and tending to her rather than handling it himself, establishing his respectful and responsible nature.

Supernatural threats from Rouge’s family’s enemies emerge, and Yusuke adapts to the upheaval despite initial unpreparedness. He commits to protecting Rouge and investigating her origins, forming a bond where he later declares her like family. His greatest fear becomes losing her, revealing deep emotional investment. Their relationship evolves through mutual trust and vulnerability, highlighted when he instinctively rushes to comfort her during a nightmare while both are minimally clothed, sharing a brief embrace that underscores a connection transcending superficial romance. He supports Rouge as she grapples with whether to regain her memories, understanding the potential consequences for her identity.

Interactions with Rouge’s sisters, Kaige and Meige, further expose his protective instincts. He becomes entangled in Kaige’s tragic backstory involving the villain Regulus. Yusuke confronts these threats courageously despite lacking supernatural abilities, emphasizing his loyalty. Financial strain and emotional vulnerability round out his character, with references to his deceased parents suggesting underlying grief. His commitment to Rouge stems from genuine care, not romantic expectation, evident in his handling of her amnesia and the dangers she brings.