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 Kuzumi is a high school student who lost his parents in an accident five years ago and now lives with his aunt, uncle and cousin Matsuri. His life seems ordinary apart from the fact that he cannot recall his early years. While he is napping, a red-haired girl named Mikoto falls on him out of the sky and takes him for her younger brother, Yuusuke. Naoki's era turns out to be a temporal refuge for people from a future where many suffer from an incurable illness, and Mikoto has traveled back in time after learning that Yuusuke was brought there. She transfers into his class, and his routine days slowly start to shift. Adapted from an August Soft game, the short-format series mixes comedy, drama, romance and science fiction.