Yuichi Aizawa, a 17-year-old high school student with a light complexion, hazel eyes, and short brown hair, alternates between a dark green jacket and his school uniform. His demeanor balances casual friendliness with a penchant for teasing, occasionally bordering on insensitivity, yet he reveals unwavering loyalty and protectiveness toward those he cares about. Fragmented memories of a snowy childhood haunt him, resurfacing as he reconnects with figures from his past—clues to a history where he unknowingly shaped their lives long ago.

After a seven-year absence, Yuichi returns to his hometown to live with his aunt and cousin, Nayuki Minase, following his parents’ move overseas. There, he intertwines his fate with girls grappling with supernatural and emotional trials: aiding Mai Kawasumi in confronting vengeful spirits, standing by Makoto Sawatari until her tragic demise, subtly diverting Shiori Misaka from suicide, and assisting Ayu Tsukimiya in recovering a cherished keepsake tied to her identity. His forgotten bond with Ayu—rooted in a childhood promise and her coma after an accident—anchors his journey, culminating in a rekindled romance that bridges past and present.

In crossover narratives, Yuichi navigates diverse worlds as a sardonic, unpredictable mediator among protagonists, blending humor with reluctant leadership. Though adaptable to shifting realities, his core traits endure: sharp wit, teasing charm, and a pragmatic approach to chaos. His growth centers on confronting repressed guilt over Ayu’s accident, reconciling fractured memories, and anchoring the emotional arcs of those around him, often serving as their steadying compass.

Averse to heights and indifferent to sweets, Yuichi’s quirks contrast his gradual acceptance of the town’s supernatural undercurrents. His role hinges on bridging humor and sincerity to resolve conflicts, channeling his own unresolved past into a force that uplifts others, even as his internal journey remains tethered to the shadows of forgotten years.