Hourglass of Summer Colors (2004)

Makimura Koutarou has made up his mind: during the summer vacation, he is going to confess his love to the seemingly unapproachable Serizawa Kaho. Yet, on the night before, he has a run-in with a strange girl - an encounter which propels him into the future. There, he learns that not only has Kaho-chan become his girlfriend, but she has also died in a tragic accident. Returning to his own time, Koutarou sets out to change the future and save his love.

Unfortunately the movie Hourglass of Summer Colors is not yet available on HBO Max.