Like Honey, he is primarily a multi-player only character, existing to fill up a slot in the roster, rarely taking part in the games's plots.
In the past he defeated and embarrassed Denta, and since then, Denta has considered him a rival, although Kotetsu himself doesn't remember when and what happened between them (ironically, even wanting revenge, Denta himself doesn't remember what happened either). He left his father's home to train under Honey, who trains him by making him do everything she wants. She also punishes him with verbal and physical beatings. With this, he is somewhat afraid of her, but holds her in high regards.
In his first appearance, in Super Bomberman 4, he was in a ship with White Bomberman, Honey, Black Bomberman, and fellow bombers when Bagura summoned the Four Bomber Kings and Bomber Great to send the ship and all the passengers back in time, to get revenge on White Bomber. Kotetsu was sent to the Edo Period and imprisoned in a cage by Jet Bomber, but in the end was rescued by White and Black bomberman and returned to his time after the fall of Bagura.
In Neo Bomberman, he was one of the many combatants who gathered together for the Bomberman Tournament. Bagular arrived in a mechanical machine and kidnapped him. he was trapped in a cage until finally being released by White and Black Bomberman.
In Saturn Bomberman Fight!!, he and Honey were invited to a tournament known as the "Bomber Convention", a tournament of the 18 strongest bomb warriors in the world that would grant one wish to the winner. Both decided to participate because it would be good for Kotetsu's training (in reality Honey wanted vast riches, such as a reward for capturing Golem Bomber), but in the end both lost.
Kotetsu is a traditional, serious, polite and chivalrous samurai, speaking in polite, archaic dialect and holding honour and dignity in high respect. He is the opposite of his master. Only liking fair fights, he holds back when fighting women and children.
- Kotetsu can attack and make shock waves with his sword to scatter the items of his enemies. There is no penalty on Kotetsu for using his sword.
- In Super Bomberman 4 there are disguises of Honey and Kotetsu. The player receives one extra hit point, but they can only kick bombs.
- In Neo Bomberman, pressing B and then up on the joystick will make Kotetsu warp to a random open position on the map in order to escape from danger.