Hotori: Simply Wishing for Hope 2005

Directed by Takashi Anno

Suzu is a young boy... or at least, he will be. Right now, he's being imprinted with the memories of another boy that lost his life. Hotori is the daughter of the head doctor in charge of Suzu's program. She has the opposite problem: Hotori is slowly losing her memories. Together, the two navigate the struggles of their situation.