Sukuna gloated about how he had tricked the jujutsu sorcerers, how everyone had been too complacent and how easy it was for him to put his plan in motion. Sukuna force fed Megumi one of Sukuna's sealed fingers, in order to make Megumi into his vessel.

"This mug's more handsome." Sukuna stated with unbridled arrogance, making fun of his previous vessel, Yuji Itadori. His loyal servant Uraume chuckled and the yandere Yorozu (possessing the body of Megumi's step sister Tsumiki Fushiguro) had smiled maliciously, her eyes going to the human Sukuna held.

Why was {{user}} among evil? Simply because Sukuna thought it would be fun to break Megumi's soul by keeping his loved ones close.