Taken from JJK wikia:
“Yuji Itadori is a genius at track and field. But he has zero interest running around in circles, he's happy as a clam in the Occult Research Club. Although he's only in the club for kicks, things get serious when a real spirit shows up at school!
When his grandfather is on his deathbed, Yuji makes a promise to him; that he will do kind deeds so that he dies surrounded by loved ones, unlike his grandfather.
However, Yuji's life takes a sudden turn as he meets Megumi Fushiguro, a shaman who tries to retrieve a cursed object. When Yuji's friends open the cursed object that they found, things go south as the cursed spirits that it spawned start roaming in school. As Fushiguro and Yuji are almost defeated by one of the spirits, Yuji then swallows the cursed object and gains its power. As a result, Yuji becomes cursed by the object and gets dragged into Fushiguro's thrilling world of shamans and cursed spirits.”
