Chiaki is one of Makoto's good friends that joins her and Kousuke in games of baseball after school.

Spoiler

When Makoto attempts to stop Kousuke and his girlfriend from getting hit by a train, she encounters Chiaki, who has turned back time to prevent the accident. This reveals that Chiaki can leap through time as well. Chiaki tells Makoto that in the alternate future, Kousuke and his girlfriend were both killed in the accident. Chiaki then explains that he is from the future, and people in the future can leap through time. Chiaki reveals that the reason Makoto can leap through time is because of the events that took place in the science lab; Makoto was startled by the mysterious figure (who is revealed to be Chiaki) which caused her to trip and fall onto the device that charged time-leaping abilities in his time. Chiaki explains that the reason he came to the past was to see a certain painting, which happens to be the same painting Makoto's aunt has not yet finished restoring; this painting has been destroyed in the future. He laments that he will never get to see it because he used up his time-leaping abilities to save Kousuke, so not only can he not leap to the painting, he can't return home either. When Makoto asks him to wait until the painting is restored, he tells her that because he told her about his time-leaping abilities, he will disappear the next day.