Atomic Samurai lures several monsters and kills them all with his Flash Attack. To the hero's surprise, a monster, revealed to be Sword Devil Executioner, managed to survive his attack. The monster notes Atomic Samurai's strategy, complimenting his power and then launches a series of swings, but Atomic Samurai parries all of the swings with minimal effort. The monster claims to be Atomic Samurai's equal, but the hero quickly proves him wrong by slicing him into dozens of pieces, killing him.
Atomic Samurai wonders if that is everyone and jokingly asks for anyone who's still alive to raise their hand. Surprisingly, a hand shoots up, the hand being G5's. The machine had allegedly finished acquiring all of the swordsman's battle data and also copied all his techniques. He states that any resistance is pointless and asks for Atomic Samurai to present him with his neck. The hero swings his swords and begins the battle, with the robot mirroring it.
Atomic Samurai and G5 exchange several parries, and the hero is impressed by G5's abilities, sarcastically noting that modern toys are very well-made and that he should order one online. G5 tells the hero that his arrogance won't last, and says that he will increase his speed. Atomic Samurai mockingly yawns and tells G5 to increase his speed, also saying that he thought he'd finally found a sparring partner for his disciples.
G5 goes on to say that his true ability is altering and upgrading any techniques he acquired. As a robot, he says he's able to bypass the limited range of motion that human joints possess, meaning that he can create all-new, previously unseen sword techniques. G5 calculates a mock battle with his computing systems and determines that 23 attacks remain before the hero's torso is severed, and unleashes his maximum speed.
The seconds pass, but the hero is still alive; Atomic Samurai notes this, saying that 23 moves have passed and he's still alive, recommending that the robot recalculates. G5 is shocked by this revelation, while Atomic Samurai explains to him that all the abilities G5 has are great, but he'll need a lot more to reach the hero, and in the end, G5 is missing the fun factor. Atomic Samurai quickly overwhelms the machine and slashes him into several pieces. However, Atomic Samurai realizes he didn't cut its core and notes there's something extra hard on the inside.
G5's body explodes, but its core robot launches a laser at Atomic Samurai. The hero parries the energy beam, and strikes with his Air Blade. Unfortunately, it wasn't able to kill G5's core, and the machine escaped. Atomic Samurai decides not to pursue G5 and leaves it to the surface, noting that they are capable. He also notes their improvised teamwork is better than what the S-class heroes have going on, and continues walking through the labyrinth of the Monster Association.
After defeating G5, Atomic Samurai continues walking through the headquarters until he comes across Black Sperm chasing Tareo as he prepares to kill the child, beginning their battle.