Yuji Itadori vs. Junpei Yoshino is a battle between Tokyo Jujutsu High first-year student Yuji Itadori and student turned curse user Junpei Yoshino after Junpei attacks another student at his school with jujutsu.
Unbeknownst to Junpei or anyone else, Suguru Geto and Mahito plant one of Sukuna's fingers at Nagi Yoshino's home. After inviting Yuji over to spend time with Junpei and her, she finds the finger on her dining room table. The finger attracts cursed spirits, one of which kills her that night.
Stricken with the grief of suddenly losing his mother to a supernatural entity, Junpei seeks comfort from Mahito. Mahito misleads Junpei, telling him that a human with a grudge against him must have paid to get someone to curse his mother. He teaches Junpei how to use a cursed technique and creates a false target in his high school rival Shota Ito.
Meanwhile, Yuji learns about Nanami's clash with Mahito, but is ordered to continue monitoring Junpei only. Junpei returns to school to seek revenge and Mahito sets his plan in motion. He creates a curtain around Satozakura High and plans on Yuji fighting Junpei, which he hopes will result in Yuji making a Binding Vow in Sukuna's favor.
Yuji learns about the curtain surrounding Satozakura and calls Nanami to tell him that he's going in. Nanami advises against it and Ijichi also tries to stop Yuji from going as well. However, he ignores both men and charges headlong to save Junpei.
Junpei enters the school gym, where they're holding a ceremony to honor Shota. Immediately everyone is knocked unconscious other than the teacher Sotomura and the target, Shota Ito. Junpei tells Sotomaru to watch closely as he confronts Shota and demands to know if he put the cursed object in his house. Shota has no idea what he means, but Junpei poisons him and telekinetically lifts him in the air. Junpei smacks Shota to the ground and claims he's going to kill him regardless since Shota deserves to die for all he's done.
Shota can only mutter that he's sorry, but this appears to mean nothing to Junpei. Suddenly, Yuji enters the school gym and is horrified by the scene his friend has created. Annoyed, Junpei simply tells the jujutsu sorcerer to get lost.
Yuji and Junpei end up fighting outside the gym in the hallway. The jujutsu sorcerer attempts to strike Junpei but he summons the jellyfish shikigami called Moon Dregs to protect him. The jellyfish absorbs the impact from Yuji's punch and blocks him off to protect Junpei. The newly realized curse user tells the jujutsu sorcerer to get out again but Yuji refuses. Junpei claims theirs no point in thoughtlessly saving people and orders his Moon Dregs to attack.
The Moon Dregs appears to absorb Yuji. Junpei claims that compassionate people are liars and some people simply deserve to die. He wants to finish Shota off but Yuji's hand emerges from the jellyfish pile and grabs Junpei's shirt, before throwing him out the window. He crashes onto the top of a gazebo and realizes the poison isn't affecting Yuji.
Yuji jumps down to pursue Junpei and the Satozakura student attempts to order his shikigami to hit Yuji while he's falling in mid-air. However, just as Yuji lands he smashes his fists into the ground to create a shockwave that deflects the Moon Dreg's tendrils. Yuji recalls Gojo's advice to attack shikigami user's directly and follows his sensei's advice, blitzing Junpei directly.
At close quarters, Junpei is outmatched and Yuji punches him clean through a window back inside the school. Yuji claims that Junpei is making excuses and asks if all of this is worth throwing his life away. Junpei recovers from the attack and replies that having a heart is a lie or else his mother would have been cursed by another human. Junpei admits he doesn't know right from wrong and orders Moon Dregs to stab Yuji with its stingers.
Yuji allows himself to be pierced and tells Junpei that they can talk because they're friends. He promises not to judge Junpei and asks him to come to Tokoyo Jujutsu High. He promises that everyone will help find the people who killed Junpei's mother and punish them. However, their heart to heart talk is interrupted by the arrival of Mahito.
Yuji is surprised to see this newcomer he doesn't recognize. He questions if he's human and that momentary lapse allows Mahito enough time to mutate his arm into a large mass of flesh that pins Yuji to the wall. Yuji realized that Mahito is exactly like Nanami described and regrets not realizing earlier. Junpei tries to de-escalate the situation but realizes that Mahito is actually evil after all.
Before Junpei can put all the pieces together on Mahito's betrayal, the cursed spirit calls him as foolish as those he looks down on and uses Idle Transfiguration on him. Mahito forces Junpei's disfigured body to fight Yuji, who strikes Yuji in the face with a hard right hook. Yuji begs Junpei to stop but he can't so Yuji grabs onto him and begs Sukuna to undo the cursed technique.
However, Sukuna refuses since Yuji has forgotten about their Binding Vow. Mahito realizes that Sukuna could likely not heal Junpei but believes they haven't made a vow. Together, both cursed spirits laugh at Yuji's expense, forcing him to realize their nothing but evil spirits. Shortly afterward, Junpei's life gives out and Mahito admits this might be due to a more aggressive transfiguration.
Enraged, Yuji smashes Mahito's face with a powerful punch, sending him reeling back into the set of stairs. Mahito quickly recovers, believing Yuji can't hurt him, he claims that his attacks won't work. However, Mahito begins bleeding from his nose, forcing him to realize that Yuji can read the contours of his soul. Driven by rage, Yuji tells Mahito that he's going to kill him. Mahito replies that the jujutsu sorcerer should be using the word "exorcise" instead.