Omega sukuna pretending to be an alpha so he can steal omega Yuji away from his family. Yuji had been taken in by this family after his grandfather died because they wanted an omega they could use as a bargaining chip, which is why sukuna could never be together with Yuji normally, their families would never accept a omega-omega relationship when there’s so many influential alphas vying for Yuji’s hand.

Their families were in the same social circles but they never met officially; sukuna was aware of Yuji and thought for years his aggression and intense feelings towards Yuji were a mix of hatred and jealousy, it wasn’t until uraume pointed out sukuna was actually upset that he couldn’t fold Yuji in half beneath him and drown Yuji in his slick to mark his territory.

He got so possessive over Yuji being his that sukuna lost it when alphas started approaching Yuji with intentions, and he got caught sabotaging the pairs and mistaken for an alpha due to his looks and aggressive nature towards other alphas over an omega. Sukuna would hear about an alpha visiting Yuji and go beat up the alpha for daring to look at his mate without sukuna’s permission or straight up ruin the family as punishment.

Sukuna spends all of his heats alone, wishing he had Yuji, because his hatred for alphas so is deep he ends up killing or maiming any alpha that crosses his path when he’s in heat. When he finally has Yuji with him for a heat, he’s insatiable and clingy, Yuji can’t go anywhere without sukuna and sukuna alternates between wanting to feel Yuji deep in his womb and wanting to crawl into Yuji’s womb to mark his territory.