Seiji Shishikura/Synopsis

Provisional Hero License Exam Arc
On the day of the Provisional Hero License Exam, Shiketsu High School students arrive at Takoba National Stadium together. Fellow student Inasa Yoarashi notices U.A. students chanting "Plus Ultra" and crashes it. Seiji Shishikura reprimands Inasa and tells him he shouldn't burst into other people's group. Inasa emphatically apologizes and Seiji tells him to leave with the others.

The Shiketsu students change into their hero costumes and meet with the hundreds of other students inside the stadium for orientation. After Yokumiru Mera explains the rules, the first phase of the exam begins and the Shiketsu students split up. Seiji ends up in the city district of the arena and uses his Quirk to knead several students into balls of flesh. Katsuki, Eijiro, and Denki happen upon this area and Seiji attacks them immediately.

Seiji sends a mound of flesh at Katsuki but Eijiro jumps in the way and gets hit. Seiji transforms Eijiro into a ball of flesh and tells the other two U.A. students that his actions are simply a show of power. He says that Shiketsu students are obligated to wear their uniform hats while working as heroes because all of their actions are crowned in tradition. Seiji believes U.A. students like Katsuki lack this level of dignity and this makes his vulgar and ordinary.

Katsuki brushes off Seiji's monologue and insults his eyes, angering the Shiketsu student. Seiji says he has a lot of respect for U.A. but the students of Class 1-A ruin its dignity. Katsuki replies that Seiji needs to speak more with his actions rather than his words. Seiji is provoked into attacking and says that Katsuki is the perfect example of the aforementioned stain on U.A.'s reputation. Katsuki counters Seiji's flesh ball attacks with his AP Shot: Auto-Cannon Ultimate Move and breaks the flesh apart with rapid-fire beams.

Seiji laments allowing himself to get provoked and regroups after falling into Katsuki's trap. He calms down and decides to crush Katsuki's pride to force him to reflect on his actions. Katsuki rushes to attack and Seiji sends his flesh attacks at him. Katsuki blows them apart with his AP Shot attack and explosions. Denki shoots two orange disks at Seiji and he avoids them. He calls Denki an eyesore and threatens to turn him into a meatball.

Katsuki demands Seiji not ignore him and attacks with another AP Shot. Seiji blocks it with a meat shield and says he hasn't been ignoring him. In fact, Seiji floated a mound of flesh beneath their elevated battlefield and used it to flank the U.A. students. A flesh attack lands on Katsuki's back and Seiji reminds him of what happened to Eijiro and calls checkmate. Katsuki is transformed into a ball of flesh and Seiji calls him pathetic.

Seiji reminds Denki that this is a show of power. He explains that he wishes to aid the examiners vetting process by eliminating unworthy heroes himself. Denki finds it odd that Seiji would prioritize this over passing, but Seiji says it's odder for the number ordinary heroes to grow. Seiji reveals that people who have been turned into flesh balls retain their sentience. So if Denki uses his Electrification Quirk, he'll hurt his allies.

Denki tells Seiji he wishes he would stop spewing insults. Seiji replies that Denki has some self-awareness to his own flaws but Denki actually says he meant stop insulting his friends. Seiji attacks with his floating flesh but Denki counters by throwing a grenade at Seiji. Seiji barely dodges the explosion and is confused as to how something detonated with Katsuki immobilized. He quickly realizes that Katsuki gave Denki a grenade just before he was turned into a meatball.

Denki tells Seiji he stumbled into a great spot and then shoots electricity through him using his new Sharpshooting gear. Seiji happened to walk in front of the two disks Denki launched earlier and they act as conductors for Denki's electricity, allowing the electric current to pass through Seiji's body and severely injure him. Seiji falls on one knee and reals from the attack. He starts to lose his grip on the people he turned into meatballs and they slowly revert to normal.

Denki tells Seiji that his friends try hard to be heroes and that he has no right to judge them. Seiji gets angry and yells that he's trying to get them all to reflect on themselves. Katsuki and Eijiro return to their normal forms and attack. Eijiro punches Seiji in the gut and Katsuki finishes him off with an explosion. Seiji is incapacitated for the remainder of the first phase and fails the exam as a result.

At the start of the second and final phase of the licensing exam, Seiji watches from the stands. He talks to what appears to be a Shiketsu teacher about Inasa's lack of experience and patience. The teacher says Seiji is the only Shiketsu student who has failed so far and he needs to reflect on himself. He fears Seiji's been too influenced by Stain to reform heroes. Seiji replies that its absurd that he would be influenced by a villain.

Remedial Course Arc
Seiji accompanies Inasa and Camie to the end of the provisional license training course. Although he's not permitted to take part in the class, he's granted permission to observe. Shoto Todoroki and Katsuki are also present at the exam. Camie and Inasa talk to them but Seiji warns them not to sully themselves with sub-par students from U.A. High. Katsuki taunts him for failing the first phase of the licensing exam and Seiji gets angry with him.

Before the training begins, Seiji sits with his teacher and says that Camie is a fool. The teacher argues that she's just bubbly and Seiji claims that's why the villains targeted her. Seiji is angry with himself for never noticing a member of the League of Villains impersonated his classmate. The heroes in training are tasked with winning the hearts of troubled children from Masegaki Primary School. Seiji believes Inasa's warm personality is perfect for the task and he's clearly irritated when Inasa's first attempt fails.

Seiji joins Present Mic and commentates during the trial. He tells the hero students not to allow themselves to be provoked by the children. Seiji believes the students should not respond with force and they need to open a dialogue with the children. Present Mic questions how the children have such powerful Quirks and Seiji responds. He explains that Quirks that continue to mix from generation to generation will inevitably become stronger over time. There is a theory called the "Quirk Singularity" where some people believe Quirks will eventually run out of control.

Seiji is surprised when his peers use their Quirks to play with the children. He calls it a perfect parry to the kids' aggression and says they managed to deepen their interactions with the children without breaking their spirits. The four students pass the trial and exit the gymnasium. Outside they find Seiji talking to All Might. Camie comments on it and it makes him angry since they're talking about her.

Endeavor Agency Arc
Interestingly, despite having failed the Provisional Hero License Exam, Seiji is shown alongside Inasa and Camie participating in the second session of Hero Work-Studies.

Final War Arc
With the remaining Heroes preparing for the Final War against an army of villains led by All For One, Seiji and the other Hero Course students from Shiketsu were tasked in accompanying the evacuees at U.A. through the tunnels that connected the two schools. However, since nobody showed up, they assumed that something went wrong and decided to help out in the battle. They arrived at the Gunga Mountain Ruins where the Heroes are being overrun by a swarm of Twice Doubles.

Right before Hawks was killed by All For One, Camie created an illusion to take his place, while Seiji used his Quirk to save the real Hawks from impending death, while also using his Quirk to allow Camie to ride. He tells the hero of their current situation, and their intention to help out, just as Inasa unleashes a massive Whirlwind that sucks up the Twice Double swarm.

With the Shiketsu High School students joining the war, the battle in the Gunga Mountains have has become the turning point as the Heroes are now at the offensive, as Inasa continues to suck up all the Twice Doubles along with Himiko among them, as the Heroes that have long-range attacks pour in everything they’ve got at All For One. Seiji remarks that All For One killed his father when he broke out of Tartarus and while he would like to have the pleasure of killing him in revenge, he knows they can't let themselves give into their hatred since they will be playing right into All For One's hands, and will follow in his father's footsteps to protect as a jailer.

Seiji tells the Heroes that that Izuku and Tomura have escaped the U.A. Flying Sky Fortress cage, so they must stop the chaos now at all costs, subduing Himiko and her Twice Doubless, as well as focusing all their ranged attacks on All For One.

Despite the arrival of reinforcements, All For One, in his prime, is still overpowering every single one of them. Using several thorns extending from his back, All For One unleashes a massive laser explosion, decimating the battlefield below. The Heroes, however, stands their ground, to keep their defense strong and keep attacking, especially now that he's stopped running away.

All For One monologues asking what makes them think they will emerge this time, that they lost the only one who could face him head on, and how ignorant he believes they are; with none of them being born from his golden dark age where his powers are at his peak, as some of them having witnessed All Might's rise to power, and most being born when he reigned supreme.

Hawks then realized that the Shinketsu students are using Inasa's Whirlwind to trap All For One in a makeshift cage, and tells the Heroes to fire everything they've got into the cage. As the Heroes continue firing their attacks into his Whirlwind, All For One decides to try to steal some Quirks, unleashing another onslaught of Rivet Stabs that manage to slice part of Inasa's face, taking out his left eye. Despite being injured, he states his Quirk is even stronger on windy days, and that instead of All For One's ancient glory days, he'd rather see a future built by the people he's cheering on.

While the Heroes have been attacking, Fumikage has been amassing his Dark Shadow to reach to its monstrous peak and achieved Total Release, which brings out the giant monstrous Dark Shadow out in the open, behind All For One. Fueled by his rage at All For One for trying to kill his mentor, Hawks, Fumikage uses Dark Shadow boosted by Inasa's Whirlwind to unleash Black Abyss: Light of Baldur, pulverizing All For One down into the ground.