Yutaka Takai, a 15- or 16-year-old prodigious inventor attending high school in Tokyo’s Senkawa District, constructs a jetpack-shaped time machine to reconcile the two-year age gap with his third-year girlfriend, Mamiko Abe. During a trial, Mamiko activates the device, launching herself two years into the future. Her abrupt disappearance initiates a systemic unraveling of her existence: memories of her dissolve among peers, family, and eventually Yutaka himself, despite his desperate attempts to preserve her through notes and reminders.

As time erodes his recollections, only fragmented impressions linger. Two years later, an unresolved unease haunts Yutaka, suggesting dormant traces of Mamiko’s memory. The narrative hinges on whether these remnants can awaken in time to intercept her return and avert her fatal plummet from the school rooftop.

Yutaka’s blend of technical brilliance and emotional fragility fuels his obsession with transcending societal judgments about age and maturity. His invention reflects both ingenuity and a yearning to prove himself beyond his perceived childishness, inadvertently catalyzing irreversible consequences.

A meta-reference within Gosho Aoyama’s interconnected universe—a fictional movie poster for *Wait For Me/The Santa Claus of Summer* glimpsed in *The Wandering Red Butterfly*—positions Yutaka and Mamiko as in-universe film characters, deepening their ties to broader narrative threads.

Yutaka’s name fuses Yutaka Abe, a real-life mentor of Aoyama, and Mamiko Takai, a 1980s Japanese idol, mirroring the author’s habit of weaving cultural and personal references into fictional identities.