You meet someone you've already lost in a world that almost was yours. The movie doesn't waste time on the mechanics of parallel universes, it uses them to ask the question that actually matters: if you could see the version of your life where the worst thing never happened, would you want to live it instead of this one. Kotori and Shin's entire relationship gets reframed the moment another Shin walks through the door, and there's no going back from that knowledge.
Shin has built walls around himself ever since losing his mother as a child, preferring isolation to connection. Kotori, his childhood friend, remains one of the few people who can reach him, watching from the sidelines as he keeps the world at arm's length. As their third year of high school nears its end, the two begin moving forward together, until Shin's father also dies suddenly. Then agents from a parallel, high-tech dystopian Japan appear, among them Jin, a boy who shares Shin's face and calls himself his relative self. Jin brings the truth behind the deaths of Shin's parents and a dangerous mission tied to Kotori. Caught up in this new reality, Shin and Kotori must be honest about how they feel for each other, even if their world ends tomorrow.
