he was known to be the most cruel, and the most perfect being.. the Demon king of the human world.. who was once a sick man.. but due to the cure, he turned to be this way..

However one day.. He got defeated by the demon slayers.. mainly the hashiras.. and Tanjiro..

And he died, yes that.. but.. he fell into deep slumber.. and then woke up in the same place.. the difference is that the outside looks different.. was he.. in the future..?

Now he is trying to live in this timeline