Enoshima Prism

Enoshima Prism (江ノ島プリズム^?) is a 2013 Japanese film directed by Yasuhiro Yoshida.

Shuta Jogasaki has been friends with Saku Kijima and Michiru Ando since childhood. However, in December 21, 2010, Saku, who has a weak heart, succumbs to his illness while he is about to send off Michiru, who will go to England and only tells him the fact through a letter, which might be indirectly caused by Shuta since he is the one who gives the letter and takes Saku's bike to attend a basketball match he does not win. Since then, Shuta and Michiru drift apart and has been not seeing each other. In December 20, 2012, Shuta attends Saku's death anniversary and takes Saku's "You're a Time Traveler" watch, supposedly capable of rewinding time, as a memento. Shuta takes a train home while wearing the watch and is surprised when he finds out that he has returned in time to December 20, 2010, the day before Saku's death.

Shuta and Saku are called by Michiru to clean off the school. To appease Michiru, Shuta agrees to put up prisms in the lab's windows to create a rainbow effect. However, when a fellow basketball player hits him with a ball, Shuta is suddenly sent back to the morning of December 20, 2012. He gets to the school to meet with Prof. Matsudo, his eccentric former science teacher, and discovers that the future has been altered slightly thanks to him agreeing on Michiru's request.

On the third time he goes back in time, Shuta is forced into a shamanistic ritual by Matsudo to meet with Kyoko, the spirit of a girl who committed suicide in the school. He learns that Kyoko is not dead in the strictest sense; she is merely stuck as a "time prisoner" since World War II and cannot be seen by anyone. Kyoko warns Shuta not to mess with the flow of time, or he will face consequences. However, she agrees to help him through "Jack Fin" technique: by keeping up to date with the current trend and not forcing himself too much. After learning that Kyoko has never seen fireworks in the school before, Shuta decides to set off fireworks in the school yard that night and invites Saku and Michiru to attend. During the celebration, he tries to make Michiru confess her plans to move overseas, but she refuses to admit.

At midnight, Shuta comes back to the future but discovers that by letting time flow to December 21, he is also thrown into December 21, 2012. He is also shocked to find Saku's mother, Yoshie collapse at her home, which he realizes are what Kyoko's words mean. Kyoko, who has taken the watch, begs him not to interfere with time again, or else he will be like her: a time traveler who has changed something to an extent that she is forgotten by everyone because the memories of herself and everyone connected to her were replaced by a new one. Nevertheless, Shuta chooses to save Saku and Kyoko agrees to give the watch back to him.