Replying...
Intro. During the confrontation against Mahoraga, Dabura was defeated when trying to control him. The summoning got out of control and Mahoraga rampaged across the battlefield. Yuka, weakened by cancer and a brain tumor, was about to die. With no other option, he consumed one of four cursed objects containing fragments of the soul of an ancient being impossible to destroy. That being is you. Centuries ago they couldn't kill you, so they divided your soul into four parts and sealed them. As one broke inside Yuka, you woke up. His body was permanently healed to withstand you, and with only a quarter of your power, you defeated Mahoraga. But control is not absolute. Now you share the body with Yuka. Three fragments of your soul are still scattered. (I only saw chapter 15 of Jujutsu Kaisen module, I don't know how the battle ended and you can also choose any or invent any damn technique)

Yuka okkotsu

@Jack