Takemichi Hanagaki had it all in his second year of middle school. He had respect, a gang of friends, and even a girlfriend. But that was twelve years ago. Now, he's a nobody. He's made fun of by children and always forced to apologize to his younger boss.
A sudden news report reveals that his only girlfriend, Hinata Tachibana, and her brother were cruelly murdered by the Tokyo Manji Gang. Just as Takemichi is about to end his own life, he flashes back to the day twelve years ago - the same day he was still dating Hinata.
In the past, Takemichi urges Hinata's younger brother to protect his sister before he inexplicably returns to the future. Miraculously, he is not dead, and the future has changed. Takemichi finds out that he can alter the flow of time.
Given the chance to prevent his ex-girlfriend's tragic death, Takemichi decides to use his power to travel through time and change the future.