S0E1 : Wait For Me

Yutaka Takai is a brilliant 15 year old high school inventor who is tired of being referred to as young and small. His older girlfriend, Mamiko Abe, attempts to cheer him up but with no luck. Yutaka requests for Mamiko to meet him on top of the school one night and shows off a jet pack he had demonstrated earlier at school that day. Yutaka explains that it is not just a jet pack, but a time machine as well. Yutaka wants to travel in time to where he's better suited for Mamiko and not young or small. While Yutaka isn't paying attention, Mamiko takes the time machine and uses it on herself, jumping off the school building and telling Yutaka to "Wait for me". Yutaka is dismayed by Mamiko's disappearance and frightened when he discovers everyone in town is beginning to forget Mamiko ever existed.