A mysterious group called Humarize strongly believes in the Quirk Singularity Doomsday theory which states that when quirks get mixed further in with future generations, that power will bring forth the end of humanity. In order to save everyone, the Pro-Heroes around the world ask UA Academy heroes-in-training to assist them and form a world-class selected hero team. It’s up to the heroes to save the world and the future of heroes in what is the most dangerous crisis to take place yet in My Hero Academia.

It is August 12th. After the remote control to his boarding house's only air conditioning unit is inadvertently destroyed by spilled cola, "I" devises a plan to return to yesterday in a time machine to recover the remote before it breaks. However, his prankster friend Ozu cannot resist playing with past events, even if it means bringing the universe to the brink of destruction. Now "I" finds himself racing through time to avoid disaster.