Hibari Kyouya travels in time and takes over the world.

“Would you believe that I’m a saber spirit?” the ghost asked. “Or maybe an ancestor?” “No,” Nie Mingjue said. He did not put down the exorcism talisman. The ghost sighed. “Well, it was worth a shot.” Before Nie Mingjue could do anything more, the ghost rushed at him – taken aback, Nie Mingjue flinched, and when he opened his eyes again the ghost was gone. He still pinned the talisman onto the swaddling wrapped around his baby brother, who was grumbling in sleepy dissatisfaction at having been nearly woken up. He wasn’t taking any chances with his brother’s health.

Wen Ning has lived as a sentient fierce corpse for about four hundred years. Going back in time could have been an accident, but isn't.

For most people, dying and waking up in your eight-year-old body is a second chance at life. For Dabi, it is a chance to make his shitty father’s life a living hell. Or: Dabi sucks at this whole time travelling thing. In his defence though, there’s really not much a kid can do in the grand scheme of things… or so he thought.