Kamikaze started a dojo before the founding of the Hero Association. However, he only approved a trio of standout disciples to work with him as heroes. Bushidrill, Iaian and Okamaitachi were 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.
Atomic Samurai first greets Bang, Genos, and Saitama enthusiastically as they arrive at the Hero Association meeting, although he notes that he does not know who Saitama is. Bang likewise acknowledges him and Saitama moves to shake his hand, which Atomic Samurai deftly denies, stating that he will acknowledge Saitama only when he has made it up to S-Class on his own.During the meeting, Atomic Samurai wonders if Bang will teach Saitama and Genos martial arts, thinking that they will make decent rivals for his own disciples.
Later, after A-City and a would-be opponent Sky King are destroyed by the newly arrived Dark Matter Thieves, Atomic Samurai's disciple Iaian enters a skirmish with Melzargard. After Iaian loses his left arm, Atomic Samurai intervenes by attacking the alien. Realizing the heavy wound of his disciple, he vows to not allow Iaian's swordsmanship to end in this tragic way.
Atomic Samurai then engages Melzargard in combat alongside Bang, Metal Bat and Puri-Puri Prisoner. During their fight against Melzargard, Metal Bat exposes its weakness by destroying the vital marble that allows him to regenerate, thereby allowing the four S-Class heroes to successfully counterattack. However during the battle, Atomic Samurai is surprised to see Bang, who was caught off guard during his counterattack, get sent flying across the battlefield by a direct blow received from the monstrous alien. When Bang got up unhurt, Atomic Samurai slashed the monster and Bang destroyed the last marble inside.
After the monster was defeated, the spaceship that was above them started to crash down. Atomic Samurai helped Iaian run towards the Hero Association Headquarters. Sweet Mask appears, demanding an explanation on why the city is in ruins. Atomic Samurai explains what happened, but wasn't good enough for Sweet Mask.
Kamikaze attends a meeting of the Council of Swordmasters. At the meeting Atomic Samurai asks the council members for help in catching and killing Garou in worries that Bang might fail and die. The council members agree, except Haragiri who mocks Atomic Samurai's plea. Haragiri proceeds to show them the Monster Cells and reveals he had received them from the Monster Association and transforms into a Mysterious Being himself. Haragiri then orders the other to eat the cells or he will kill them, but Atomic Samurai cuts him first, killing him.
Afterwards, Kamikaze and his three disciples, Bushidrill, Iaian and Okamaitachi went on a search and destroy mission to find the Monster Association's base. They searched through the mountains, killing any monsters they come across.
Kamikaze and his three disciples arrive at the Hero Association. They are put on stand by as preparations for the invasion of the Monster Association unfold. Sweet Mask antagonizes them dismissing Kamikaze as weak much to his anger.
The S-class heroes, Kamikaze, Tatsumaki, Child Emperor, Pig God, Flashy Flash, Superalloy Darkshine, Zombieman, Puri-Puri Prisoner and Sekingar attend a meeting and they reassure Narinki that they will rescue his son. They each receive a transmitter that will show their location to each other. During the meeting, Kamikaze asks how Puri-Puri Prisoner will turn the monsterized prisoners back to human. Kamikaze mentions to Sweet Mask that he's bringing his three disciples to the underground rescue operation. Kamikaze sees King without the King Engine running and believes he is focused. He leaves with various heroes to attack the Monster Association.
Kamikaze arrives within the ghost town of Z-City . There he battles the Monster Association's initial monster attack. He kills the now Demon-level monster Rhino Wrestler and cuts down several other monsters.
Later, Kamikaze battles and defeats several monsters including Sword Devil Executioner and G5. G5 proclaims to have analyzed Kamikaze's battle style but is quickly defeated and escapes. Kamikaze decides to leave G5 for the surface team to deal with and continues his advance.
Kamikaze communicates to the heroes that he discovered another child and goes after the him. Kamikaze encounters Black Sperm. Feeling confident, Kamikaze brags to the monster on his easy victory much to Black Sperm's ire. They battle and Kamikaze discovers Black Sperm's splitting ability. Kamikaze is forced back with Black Sperm's onslaught and unleashes his new skill Focused Atomic Slash. The hero disintegrates several Black Sperm clones and leaves to chase after the child but is stopped cold by the main collection of Black Sperm. As a last ditch attempt, Kamikaze brings the ceiling down on both of them.
Kamikaze is later seen defeated and at the mercy of Black Sperm.  However, he is saved when Tatsumaki tracks his position using his transponder signal, and she protects him in a psychic bubble. With his last act, Kamikaze performs an Atomic Slash on Black Sperm before floating towards the surface of Z-City.
Atomic Samurai talks with Bang about Bang's retirement. He is shown thinking about what he will do without Bang, and questions if he should try his luck with King.
He is later seen in M-city looking for King for a duel, however, he cannot find him and proceeds to have sushi with his disciples. During the meal, he meets King at the restaurant and provokes him into a fight. After hearing the King Engine, he and his disciples mistakenly believe King is in battle-ready formation. During this time, King is choked because of fear, which is further misinterpreted by the others as boldness.
Fortunately for King, Kamikaze puts his sword down and praises King's boldness not before slicing an apple into pieces. After that, he forces King to go outside and begin to fight. However, during the fight, King begins to bluff nonsense about a non-existent atomic reaction, which confuses him and his disciples. At the end of his speech, King walks away and tells Kamikaze not to perform his attack since it can lead to casualty, something which the heroes don't want to happen. As the result, Kamikaze puts down his sword.
Despite that, Kamikaze urges King to cut an apple with his Katana to determine King's life and power. However, King is too nervous, scared, and weak to even pull the sword out of the sheath. As a result, King delays cutting the apple for several minutes and ultimately puts down the sword to walk away in shame. Fortunately. Kamikaze's delusions about King's reputation and power kick in and he incorrectly deduces that King cut the apple at the cellular level, faster than he can even see, stating that the apple "does not even know it has been cut."
In the end, Kamikaze praises King's fake power and asks his students to join him in honing their swordsmanship in basic training since he thinks he needs to practice more in order to surpass King. Meanwhile, King walks away in shock and anguish.