Tsunagu received an education at U.A. High School.
At some point in the past, he ascended to being among the top five Pro Heroes.
Some time ago, Best Jeanist was called into a meeting with Eraser Head, Manual, Death Arms, Snipe, Thirteen, Endeavor, Air Jet, Midnight, Ingenium, Gunhead and a member of the police force to speak about the unwilling civilians injected with Trigger.
He is one of the heroes fighting Number 6's bombers.
When Katsuki Bakugo chooses him for an internship, Best Jeanist introduces himself by admitting he does not like Katsuki very much. Irritated, Katsuki replies that Best Jeanist sent the offer to him. Best Jeanist says all his other recruits were well behaved unlike him. Although Best Jeanist admits that Katsuki has outstanding talent, he says the young man still needs to be taught how to display himself as a hero. Irritated Katsuki approaches Best Jeanist, forcing him to discipline Katsuki by using his Quirk to wrap him in denim.
The next day, Best Jeanist tries to teach Katsuki the value of maintaining an elegant outward appearance. Best Jeanist styles Katsuki's hair similar to his own, but it returns to its messy form shortly after.
After Hero Killer: Stain's defeat is published, Best Jeanist reminds Katsuki and all his sidekicks to remain calm and operate as they normally would. Later on, Best Jeanist takes Katsuki on patrol. He asks Katsuki why patrols are important, to which he answers that it is because they can beat up criminals on sight. Best Jeanist says this answer is wrong and that patrols help heroes maintain a strong public image. Katsuki ends up getting into a spat with young children, making Best Jeanist comment about Katsuki's pride.
Following the abduction of Katsuki Bakugo, Best Jeanist is recruited by Detective Naomasa Tsukauchi. Naomasa enlists Best Jeanist to the Hideout Raid Team, a fighting force tasked with infiltrating the League of Villains hideout in Kamino Ward. Alongside Edgeshot, Endeavor, Gran Torino, Gang Orca, Tiger, Mt. Lady, Kamui Woods and All Might, Best Jeanist attends a strategy meeting to rescue Katsuki Bakugo from the villains. 
The Hideout Raid mission commences the next night. Just prior to the mission, Best Jeanist reminds Endeavor that he is an alumni when the latter complains about participating. Best Jeanist shares with everyone that he had Katsuki as an intern and worries that Katsuki's attitude might get him into trouble. Gang Orca is surprised that not even the elegant Fiber Hero could get through to him.
Best Jeanist leads the second squad to the Nomu production factory. Gang Orca and Mt. Lady help him successfully secure all of the Nomu. Best Jeanist restrains the majority of them with denim strings using his Quirk. Mt. Lady complains about the simplicity of their task, but Best Jeanist explains that the difficulty of the task doesn't take away from its importance. The hideout team is interrupted when a shadowy figure appears from the dark and Best Jeanist quickly restrains the man by tightening the fibers of his clothes. Mt. Lady expresses concern for the man but Best Jeanist states he cannot give the villains any slack. The villain frees himself and aims a large explosion at Best Jeanist and the squad.
Best Jeanist manipulates his allies' clothes and pulls them out of danger. He takes the brunt of the evildoer's blast and lies injured on the ground. The man levitates towards the Fiber Hero and commends his efforts to protect the other heroes. Best Jeanist recognizes the man as the leader of the League of Villains. He knows that this man's strength is comparable to All Might's, but believes that is no excuse not to act. Best Jeanist attacks, but is easily countered and crushed by an air cannon from All For One. 
Defeated, Best Jeanist falls unconscious. He's later rescued when All Might, Endeavor, Edgeshot, and Kamui Woods arrive to defeat All For One. 
In the second annual Hero Billboard Chart JP of the year, Best Jeanist is absent, as the announcer reveals he is taking a rest from his duties as a Hero for an extended amount of time. It is also revealed he has climbed to from No. 4 to the No. 3 spot due to his participation in the Kamino Ward Hideout Raid.
At some point prior to the Revival Celebration, Best Jeanist meets with Hawks, and discuss about his health. Best Jeanist reveals he had lost a lung during the Kamino Incident, and not even Recovery Girl's help can recover the missing organ. However, this loss does not make him give up his plans of returning to the public eye.
Hawks responds how unfortunate things have turned out before brandishing one of his blade feathers at Best Jeanist.
Later, it is revealed that Best Jeanist has gone missing, and that his sidekicks haven't heard from him in some time.