Hiram, the most powerful demon king in history, ruled over all the demon tribes. He defied the Demon God's demand for sacrifices and lost his life after fierce battle. The demon tribe will never defeat Demon God while living under its control. As long as this was the way of this world, there was no way to become the strongest. Five hundred years have passed since then. Hiram was successfully reincarnated as a "human" youth. Although he was said to be the "weakest", he was actually a human with high potential. To kill the Demon God this time, he began adventurous journey... (Source: Square Enix, translated)

Nearly half the population of Sakurada, a small town near the Pacific Ocean, has some sort of unique power. These powers range from being able to enter the mind of a cat, to resetting the world back to a certain point in time in the past. There is a group known as the "Kanrikyoku" that controls and monitors the use of these powers. Asai Kei and Haruki Misora work for their school's club called "Houshi" club, which execute any missions received from the Kanrikyoku. Misora has the ability to reset the world 3 days. This means that all events and any memory of the past 3 days that "could have" happened, never happened. Kei has the ability to "remember" the past. Even after Misora uses her powers to reset the world back 3 days, Kei will retain those 3 days in his memory. Combining their powers, these two solve missions issued by the Kanrikyoku. (Source: MangaHelpers)

In the near future, superhumans called Others, who have awakened to their unique abilities, are active in the world. The world enjoys peace and prosperity thanks to the overwhelming power of the Tiger's Nest, an organization of righteous Others who execute Criminal Others who use their abilities to commit crimes. However, poverty and crime were rampant in the old capital, the slums, which had been abandoned by the Nest. A lone tiger emerges from the darkness of the slums. The rebel hero, Tiger Mask, bares his fangs against Nest's justice. Now a new hero legend begins!