A girl falls out of the sky onto a boy with a broken past, and his entire life becomes the question she answers without meaning to. Naoki can't remember his childhood; she thinks he's her brother. That collision rewires everything, the show refuses to let either of them stay strangers, and it won't let you pretend the gaps in memory don't matter. What starts as absurdist romantic comedy slides into science fiction that actually earns its heartbreak because you've already invested in two people who might not be who they think they are.
Naoki has spent five years living a quiet life with his relatives, haunted by a blank spot in his childhood memories. Then a girl literally crashes into his world, claiming to be his sister and insisting she's traveled back in time from a dystopian future. Her story seems impossible, yet the evidence keeps piling up: she knows things about him nobody should know, and her technology defies explanation. Naoki learns that his era serves as a sanctuary for the sick and dying from centuries ahead, where an incurable plague ravages humanity. Mikoto's desperation to find her younger brother, who was sent back in time for treatment, becomes the thread that unravels Naoki's carefully constructed sense of normalcy. As the two navigate the collision between past and future, romance, comedy, and genuine danger weave through their investigation. Naoki must confront the gaps in his own history while helping Mikoto navigate a world she doesn't belong to, all while questioning what he's really willing to sacrifice for family and truth.