Iaian/Synopsis

History
As a disciple of Kamikaze, Iaian was recruited after an apple cutting test. As Kamikaze has the ability to tell how a person lived their life by cutting with a sword, he only recruits disciples if they pass his test. At some point in the past he and his teammates fought Child Emperor and lost.

Alien Conquerors Arc
After the destruction of A-City, Iaian climbs out of the rubble only to see nothing standing in front of him but the Hero Association's Headquarters. He later saves a father and his son from being killed by Melzargard after the father moves some rubble to get to his son. As he is standing there, the monster appears behind him and attempts to crush his head. Melzargard only crushes his helmet, its occupant having moved away in time. He states that there was no way he would not have noticed its killing intent and proceeds to attack the monster. While dodging one of the monster's attacks, his left arm was torn off. Melzargard then began splitting itself into five different forms. Feeling hopeless of his situation, the monster is suddenly cut to pieces by Atomic Samurai and Iaian was ordered to stop bleeding by his master. While the S-Class heroes are fighting the monster, Iaian advised them to retreat and find another way to kill the monster, but his pleas were futile. During the fight he witnessed Silver Fang being struck by Melzargard's attack and was surprised to see he was unharmed. After the monster was defeated, the spaceship that was above them began to collapse and Iaian was helped carried by Atomic Samurai.

Super Fight Arc
Iaian, Okamaitachi and Bushidrill are waiting outside discussing about Garou's hero hunt, while their master Atomic Samurai is attending a meeting with the Council of Swordmasters. After Atomic Samurai killed the monsterized Haragiri, Iaian noticed the smell of blood and Atomic Samurai ordered they will strike the Monster Association.

Monster Association Arc
Iaian is seen waiting for the S-Class meeting to end with his fellow disciples. Iaian is one of the heroes who fights the first wave of monsters from the Monster Association. When Rhino Wrestler appears from the 2nd wave, Iaian watches the other heroes attempt to attack the monster but fail miserably.

The A-Class hero unsheathes his sword and strikes his horn, momentarily halting the monster's movement.

Rhino Wrestler rates his attack 69 points, and the others see it as the opportune moment to strike together. First, Jet Nice Guy attacks with his Ultimate Jet Straight across the monster's face; next, Double Hole tickles his nose to activate his energy sneeze. Crescent Eyebroll uses his Crescent Consecutive Slashes, while Narcisstoic uses his Rose American Sack attack, and the rest of the heroes join in, but Rhino Wrestler is able to blow all of them away, rating each of their attacks. The heroes are shocked at his power, while Rhino Wrestler reminisces of a moment when Gyoro Gyoro conversed with Rhino Wrestler before the monster raid and how Gyoro Gyoro commended the monster for the increase in strength. Rhino Wrestler screams out for the strongest heroes to fight him, all-the-while fighting Iaian. Rhino Wrestler is able to hold Iaian back, but before the battle could continue further, Atomic Samurai tells his disciple he would take his place. Iaian insists he could handle it, but Atomic Samurai tells him he would cut off his horn himself.

Iaian, Bushidrill, Okamaitachi enters the Monster Association HQ.

Iaian, Bushidrill, Okamaitachi encounter Do-S and the mind-controlled mercenaries. They do battle but are interrupted by Sweet Mask. Sweet Mask calls for the swordsmen to leave the battle to him. The Disciples leave at first, but Iaian is worried that Sweet Mask intends to kill the mercenaries. They go back to help Sweet Mask with Do-S, and manage to prevent him from killing the mercenary squad. Iaian gets in a short argument with Amai Mask following a blunt statement from Bushidrill. Iaian intends to drop the issue after being pressed back, and exchanges a few smug remarks about his master with Sweet Mask before the mercenaries wake up. Iaian comforts the mercenaries, before saying he has a plan to get them to the surface.

The disciples and mercenaries attempt to sneak past the monsters by having the mercenaries feign Do-S's brainwashing and claim to be transporting the heroes to Orochi under her orders. However, the plan fails as the monsters attempt to eat Iaian, causing him to slice up a monster in self-defense. Iaian laments that his plan failed as he thought it would work, and the group gives up on any pretense of stealth and attacks the monsters. Iaian attempts to warn Tongara of an approaching threat, but the mercenary roughly elbows him back, although he quickly apologizes, stating that it's embedded in him due to his experience on the frontlines. Suddenly, spikes pop up from the floor of the room, injuring a few of the mercenaries. The three disciples spring into action, slicing the floor and falling through to the room below. There, they encounter Devil Long Hair, and Okamaitachi becomes infatuated with him, much to Iaian and Bushidrill's annoyance. They tell Okamaitachi to snap out of it, reminding them that their role is to lighten their master's burden. Okamaitachi attacks with his Air Blade, but Devil Long Hair stops it with his hair, shocking the swordsmen. Devil Long Hair counterattacks, but Bushidrill manages to stop the attack before any harm was done. The Demon-level monster then extends his hair toward Iaian and Bushidrill, and the swordsmen prepare for battle. The three swordsmen work as a unit, rushing in and cutting Devil Long Hair's hair as fast and as effectively as possible, and manage to defeat him, although they admit it was a difficult opponent, and had they not worked together, they surely would have lost.

After the battle, the swordsmen rendezvous with the mercenaries and attempt to sneak through another group of monsters. The plan fails again as the monsters demand a password, but they nevertheless manage to overpower the monsters. The disciples, accompanied by Tongara, chase Master Joe into a room, where Evil Natural Water, a powerful Monster Association cadre, is being held inside a tank. The unnamed monster releases Evil Natural Water from its tank, enabling it to move freely. It attacks with Mad Doctor Fish, which they manage to fend off. The heroes and Tongara attempt to retreat outside and seal the vault, but Evil Natural Water escapes and attacks Iaian with a high-pressure water jet. He deflects it, but it damages his sword. The group attempts to retreat further, but Tongara is critically injured by a water jet as he pushes Bushidrill out of the way. Iaian and Okamaitachi drag Tongara to safety as Bushidrill holds Evil Natural Water off, and the mercenary asks them to take care of his troops as his last wish. The three of them attempt to retreat, but are later seen defeated when Child Emperor finds the trio wounded and defeated. However, Iaian is still conscious, and manages to warn Child Emperor of the still lurking Evil Natural Water just in time for Child Emperor to dodge its attack.

The heroes are later lifted up by Tatsumaki's barriers, but Iaian notices that the mercenaries are still underground. He slashes through his barrier and attempts to contact Tatsumaki for her to rescue the others, but to no avail. However, he is rescued by Pig God, who also came back to rescue others. He is later regurgitated by Pig God on the surface and thanks him for the rescue. He then has an emotional reunion with Atomic Samurai, who praises him on a job well done.

After the S Class executes their plan to bring down Psykos and Orochi, Iaian and Atomic Samurai are attacked by Evil Natural Water, and Iaian draws his sword, ready for battle.

The three swordsmen are then swallowed up by Pig God, who finds them and consumes them, and manages to bring all three of them up to the surface and regurgitate them without any noticeable injuries. As Atomic Samurai watches the other S-Class heroes fighting and being unable to do anything since he lost his sword, Iaian speaks to his master and gives him his sword to fight Garou.

The Murder Case That Is Too Impossible
Iaian was invited along with the S-Class heroes to a hot spring resort, after the Dark Matter Thieves failed invasion. While enjoying himself at the hot spring, he wasn't satisfied that some of the heroes that did not participate in the battle were invited to the resort, but Bang managed to calm down the situation. The next day after the ceremony, the heroes find Zombieman murdered, stabbed in the back by Atomic Samurai's katana.

As Child Emperor interrogates every hero, Iaian was one of many alibis for Atomic Samurai so all suspicions were dropped. While the investigation wasn't progressing, Tatsumaki tried to restrain everyone, until Zombieman suddenly woke up. Zombieman later revealed that Atomic Samurai's katana was floating with green light surrounding it similar to Tatsumaki when it stabbed him. Zombieman didn't care about what happened the night prior and the heroes disbanded.

Going Fishing with Middle-aged Men
Bang asks Atomic Samurai how Iaian is dealing with the loss of his arm at the hands of Melzargard, and Atomic responds by saying that Iaian is strong, and has already started training to get adapted to fighing with just one arm.