After finding his mom killed, Satoru's time-traveling ability takes him back 18 years for a chance to prevent her death and those of three classmates.

Saigo Takamori, the hero of the Meiji Restoration, was born to a poor, low-ranking samurai family in the Satsuma domain (present day Kagoshima Prefecture). His simple honesty caught the attention of its charismatic feudal lord of Satsuma, Shimazu Nariakira. Nariakira’s assertion that the love of people is what will enrich and strengthen the nation captivated Saigo who took on Nariakira’s secret mission and eventually became a key person for Satsuma. Not a portrait of him survives today and much of his life is a mystery. He is a man who was twice exiled and thrice married. He overthrew the Tokugawa Shogunate with exceptional bravery and action. Although he accomplished the restoration, he lost his life in a fight with the new Meiji government.

Kujo Rina is a chemistry teacher and the homeroom teacher for the 3rd grade D class at Horai High School. She doesn't have a bond with her students. On the school's graduation day, Kujo Rina is pushed from the 4th floor and falls down. She is able to glimpse a school uniform sleeve on the person that pushed her. At that time, she wonders why she was pushed and that she does not want to die.