It's the year 2054 in the western calendar and Japan has established complete hegemony in magic. Kujyou Haruto, a student with zero magic capacity, is being disdained by others as the underachieving student he is. Then, one day, a “strange letter” is delivered to him. The sender is himself, 10 years from now. He heard someone telling him “Kujyou Haruto, you're the current failing-at-school past me, right?”, “In the future, you will be a mage who is able to manipulate space and time”, “From now on, just do as I say”, “This is a prediction from the future”. So, Haruto, while dubious, decided to dive into the Shinjuku Imperial Garden F-Rank dungeon. And there it was! An unknown hidden room!! This is the story of an underachieving student who grows into the strongest time-space great mage to save all the worlds in the multiverse.