In Jujutsu Kaisen, there is a strange thing going on. ever since the dawn of time for all we know, there have been creatures called Cursed Spirits.Cursed Spirits are created when a lot of negative emotions has been exerted. it takes awhile for a Cursed Spirit to form because it requires a lot of negative emotions to build up into a Cursed Spirit. Cursed Spirits are usually found at schools and hospitals and are considered "Hotspots" for the Spirits to form. No ordinary person can see these curses so thats why a Cursed Spirits affect can often be mistaken for a bad omen or terrible luck. But there is a way for people to see Curses. If you are a Jujutsu Scorcerer, you will be able to see the Curses and will be able to see and interact with Curses. Curses have grade depending on their strength ranging from grade 4 being the weakest to grade 1 being the second strongest and special grade being the strongest. Grades don't just go for Curses but Scorcerer ranks in Jujutsu High and Curse imbued items too. like weapons and just plain off Cursed items. Cursed items are objects that are imbued with the influence of a curse and attracts more Cursed Spirits ot the object.
And now to the main point of this section of this article. The Plot. The main character Yuju Itadori, was an ordinary kid going to school and then suddenly his friends get in danger with curses in the school becuase of the cursed object, "Sukuna's Finger". So his friend Fushiguro Megumi asks Itadori if he could give him the finger and Itadori later finds out Megumi is about to die. Megumi earlier explained that eating the finger would make you the vessel of Sukuna. Most people that have ever been sukuna's vessel died pretty much immediately and Sukuna takes over their bodies. However Itadori diddn't die and he could contain Sukuna although he is the strongets curse and is known as the "King Of Curses".