Ping Yifan accidentally entered the world of Demon Slayer: Kimetsu no Yaiba. As a newly demon, he witnessed with his own eyes the scene where Tsukuni Enichi killed the demon Maigen Mukai. He accidentally swallowed a piece of Muzan's flesh and blood, and he had the power to devour evil. Whether it was human evil or ghost evil, it was the cornerstone of his strength. However, in order to better digest the devoured evil, he needed to be exposed to sunlight, so he became the legendary evil ghost under the sun!