Kokichi Muta vs. Mahito is a battle fought by semi-grade 1 jujutsu sorcerer, Kokichi Muta against special grade cursed spirit Mahito. It takes place in Kokichi's hideout after his contract with Mahito and Pseudo-Geto concludes.
Mahito and Pseudo-Geto meet Kokichi in his secret quarters at an unmarked location. Kokichi comments that he was beginning to think they were going to run out on him. Geto insists they would never dishonor their end of the Binding Vow and adds that the disabled student knows better than anyone the consequences of cursed restrictions. Mahito complains about the smell and expresses his desire to kill Kokichi and be done with this.
Geto and Mahito agreed to heal Kokichi's body with Idle Transfiguration in exchange for information and cooperation from his unregistered puppets. The curse user reminds his partner that the killing doesn't come until after their end of the contract is fulfilled. He would have preferred to have used Kokichi in Shibuya and Kokichi argues they already broke the vow by injuring students from Kyoto Jujutsu High. Mahito tries to abstain from responsibility by pointing out that Hanami was the one who attacked the Kyoto students.
Kokichi has enough of Mahito's comments and demands the curse to hurry and get the healing underway. Annoyed, Mahito threatens to deform him further but Geto sternly reminds Mahito of the risks breaking a vow with another person could bring down upon them. The curse acknowledges this and reluctantly fixes Kokichi's body with Idle Transfiguration.
The long disabled young man finally has a functional body. He flexes his muscles and stands for the first time without distress. Mahito asks for some enthusiasm but Kokichi replies that celebration can only come once they've settled business. With both sides in agreement, Kokichi calls several Mechamaru puppets to his side and Mahito declares the start of the fight.
Geto asks his ally if he needs a hand but Mahito tells him to stop because Kokichi is his "toy". Several Mechamarus rush towards the special grade curse and are easily brushed aside by Mahito's enlarged arm. Changing the shape of his soul to gigantify his right arm and then reinforcing his sweeping attack motion with cursed energy effortlessly breaks the puppets apart. However, Kokichi disappears in the chaos, confusing Mahito.
Mahito surmises that Kokichi retreated without a reason to kill them. The curse doesn't feel like hunting as much as he does fighting. Suddenly, the floor caves in below Mahito's feet and the entire area implodes with a giant explosion of water. Mahito escapes the water onto a bridge. With an excited grin, he welcomes the next challenge with open arms.
Mechmaru Mode: Absolute stands towering over him and the large body of water it's standing in. Mahito is impressed the recluse student managed to build this and immediately recognizes that the most concentrated point of energy is in the head of the giant armored puppet, where Kokichi is piloting it. All functions are normal with Mechamaru but sensory feedback is blocked as well as any outward communication signals. He's been trained by curtain and surmises that Geto has to be behind it. Kokichi bets his victory on escaping the curtain and contacting Satoru Gojo for help, but he'll have to exorcise Mahito first to achieve that
All those years tied down by the bindings of his heavenly restriction, Kokichi watched everything in the world outside him. He spent all that time accumulating cursed energy and he's prepared to use all of it to win. He enthusiastically begins with a one-year charge of cursed energy and blasts apart the bridge with Ultra Cannon fired from Mechamaru's palm.
Mahito escapes the explosion by shapeshifting his feet to increase his mobility. He moves out of the smoke but half his face is charred from the attack and he wonders if his opponent is planning to keep burning away at his body. Kokichi and Mahito both know that Mechamaru's physical and energy attacks won't be effective on the curse's soul. The giant puppet throws two downward straight punches that crack the bridge apart but Mahito jumps into the large body of water and changes himself into the form a fish.
Determined to flush Mahito out, Kokichi uses a two-year charge of cursed energy that coats the entire massive puppet's body in it. Mechamaru unleashes Miracle Cannon, a double explosive cannon that generates a giant wave of water. Mahito emerges from the explosion and extends his left arm to grab the wires on Mechamaru's head. The currse won't back down and he's not paying any attention to his opponent's offense. Kokichi believes that it's finally time for his secret weapon.
Mahito contracts his left arm and strikes Mechamaru's head with a cursed energy-reinforced right hook. Kokichi is impressed with his power and admits that Mechamaru's armor will break apart if he's not careful. The puppet manipulator inserts one of his secret technique tubes into a slot on Mechamaru's dashboard activating a function called technique charge. Kokichi only has four of these and is betting on this first one. Mechamaru's right pointer finger splits open at the tip to reveal a gun barrel. Its targeting system locks on o Mahito as the curse uses wings to fly through the air. Koichi orders Mechamaru to fire and the projectile stabs into Mahito's left-wing. Initially, Mahito dismisses any sign of a threat to his soul but suddenly his wing explodes.
Vulnerable, Mahito is open hand smacked by the giant puppet's hand down into the forest area beside the lake. Mahito crashes through several trees and believes that his soul was destroyed. Before he can gather what's happened, Mechamaru unleashes a flurry of rapid-fire downward straight punches that break apart the trees in the area. Mahito avoids the onslaught by changing himself into a bird and flying away. He appears to have regenerated his wound as well but Kokichi realizes that he just changed the shape of his soul to make it look like he regenerated. The fact that the special grade is attempting to conceal his wounds is a positive gain in this fight for Kokichi.
From the sidelines as a spectator, Geto even acknowledges that Kokichi's strategies are working on Mahito. Next, Kokichi uses a five-year charge of cursed energy to fuel Pigeon Viola. It sends five giant cursed energy bullets twisting and chasing Mahito through the area. The curse changes back into his humanoid form and lands on a bridge parallel to the broken one. Most of the curse following beams crash into it and save Mahito from the impact. He remains confident all he has to do is find which offensive is effective against his soul.
However once again Mahito is caught off guard by Mechamaru's speed. He narrowly avoids another downward punching fist by retreating on the backfoot. He's unable to escape Mechamaru's next right hook, which sends the curse reeling back through the trees. Kokichi activates his second technique charge, shifting Mechamaru's middle finger into a spike. It prepares to inject the injured Mahito with it as Kokichi believes he can achieve his dream to meet up with his classmates. This fantasy dispurses when Kokichi notices Mahito's gaze and the curse open's his mouth to reveal the hand-signs for his Domain Expansion. Mahito traps Mechamaru's entire body with Kokichi inside within Self-Embodiment of Perfection.
Idle Transfiguration automatically hits within the domain and Mechamaru collapses. Mahito boasts that even a puppet manipulator can't hide while inside a domain and that he'll have plenty of cursed energy recovered in ten days for Shibuya. The curse turns his back to the puppet and believes he's won. He expresses how awkward he feels that Kokichi put far too much stock in strategy.
Once again the tide of battle shifts in Kokichi's favor. Unbeknownst to Mahito, Mechamaru rises behind him. It jabs the spiked finger through Mahito's back, piercing his torso as well. Confused, Mahito looks back to meet Mechamaru's gaze. Inside, Kokichi glares at him and activates the secret technique sealed inside the tubes: Simple Domain!
This forces Mahito's body to explode and the domain to disappear, seemingly exorcising the cursed spirit. Mechamaru roars in victory and Kokichi believes he's done it. Impressed, Geto realizes that Kokichi uses Simple Domain to neutralize Mahito's cursed technique in order to injure him. Even inside his own Domain Expansion, Mahito was still vulnerable to this. Kokichi turns Mechamaru's cursed energy beam on Geto, but suddenly the cockpit area's front section crashes open.
Shocked, Kokichi sees Mahito crawling through the hole in a multi-legged form. He takes another technique tube and tries to stab Mahito with it in a last-ditch effort. The two fighters lunge at each other and their hands pass by one another's with great speed. Unfortunately for Kokichi, he was the slower one and his dreams are taken away along with his life. Mechamaru collapses on the bridge and its broken face bleeds its master's blood, signifying both of their demises.
Mahito regroups with his partner who thinks the curse was cutting it close. Mahito claims that he exploded himself at the same time Simple Domain did and deactivated his domain to lure Kokichi into a false sense of security. It was apparently all according to plan and nothing was close about it. Mahito does admit he's impressed with Simple Domain and expresses his gratitude for getting to warm up before the big main event in Shibuya.
With their final preparations finished, Geto announces they adjusted the terms of the commissioned curtains his curse users will be using. There should be no issue endowing them with the ability to use them either. Just over a week later, the fateful day in Shibuya finally arrives.