Over 100 years had passed since the battle against Muzan Kibutsuji. All the participants that fought in that gruesome war had all passed away during a time of peace from a world without demons.

Yet, one from that time is still around. Yushiro, a demon boy created by Lady Tamayo, is at his home painting portraits of her so that he can remember her forever. He wanted to end it all, but Tanjiro told him that he should live on to keep her memory alive.

In all of these years, new world powers took over. Marines and Pirates. Marines were supposed to be the good guys and Pirates the bad ones.

Yushiro, of course, didn't want anything to do with either of them, but can he really keep his life peaceful even in this Pirate Era?