You spend the whole series pretending this experiment doesn't matter, that these connections are temporary, that walking away will be easy. The Final Arc spends four episodes proving you were lying to yourself. It doesn't have time to waste on plot, it burns everything for the moment Arata realizes he's already changed, that the people he met have already changed him back, and that forgetting them won't undo any of it. The pacing is suffocating, the adaptation skips massive chunks, but the show knows exactly what it's selling: the specific devastation of having to leave people who saved you, knowing they won't remember you saved them too.
Arata Kaizaki has spent a year reliving high school through a secret experiment that's given him a second chance at life. Surrounded by genuine friendships and unexpected connections, he's rediscovered parts of himself he thought were lost to adulthood. But reality has a cruel deadline: when the program ends, everyone he's bonded with will forget he ever existed. His handler keeps reminding him that none of this is permanent, that the relationships he's built are just part of the illusion. Meanwhile, Chizuru Hishiro faces the same countdown. After two years in the ReLIFE program, she's transformed from a detached observer into someone capable of real connection. Both subjects know the end is coming. Both have changed irreversibly. The final arc asks whether the memories matter when they'll be erased, whether the person you've become stays with you even after everyone forgets who you were.