When Yuji Itadori swallowed a cursed finger, he trapped the evil Ryomen Sukuna inside his body and started Jujutsu Kaisen off with a bang. Since then, the show has seen Yuji and the rest of the Jujutsu Sorcerers set out to vanquish more Cursed Spirits and locate the rest of Sukuna's fingers which they hope will allow them to kill Sukuna once and for all.
Source：https://www.cbr.com/jujutsu-kaisen-how-strong-is-sukunas-true-form/
