Genos vs. Deep Sea King

Genos vs Deep Sea King was the battle between the S-Class Hero Genos and the Deep Sea King, a Demon-level monster.

Prologue
The scene reveals that the four heroes were utterly defeated by Deep Sea King's superior prowess, and the civilians cower in terror at Deep Sea King's seemingly unstoppable power. Just as Deep Sea King is about to prey on the human bystanders, Genos arrives on the scene, and their battle begins.

Battle
Just as the Deep Sea King prepares to kill the civilians in the stadium, Genos crashes through the top of the stadium. As the Deep Sea King turns to face him, Genos quickly states he will eradicate him, and launches a very powerful punch at the Deep Sea King, creating an energy wave that breaks through the wall of the shelter and destroys the buildings behind Genos. The whole shelter echos with applause and Genos comments on how desperate they were to be saved, when suddenly the monster grabs Genos's arm and slams the hero with a powerful right hook, sending him into the wall and ripping off one of his arms in the process. The Deep Sea King, whose face has a hole from Genos' punch, says he will tear Genos to shreds, while Genos, with a cracked face from the impact with the wall, is disappointed in himself for again letting his guard down and never learning from his mistakes.

Genos shouts for everyone to evacuate and leave the mysterious being to him. The Deep Sea King grins maliciously at the people and shouts that they cannot escape. Genos surges with energy, then propels himself toward the Deep Sea King and kicks him square in the face, with the Deep Sea King matching his blow with a strong punch. The two combatants exchange a barrage of punches, both of them seemingly equally matched, despite Genos only having one arm. Genos quickly gains the upper hand and lands a hard blow to the Deep Sea King's face. While he is distracted, Genos continues his assault and attacks with a very powerful uppercut, sending the Deep Sea King crashing up through the roof. Genos follows this up with his incineration cannons, which seem to disorient Deep Sea King.

He quickly shrugs off the enveloping flames, but not before Genos hovers above him and uses a new move, "lightning eye", temporarily blinding Deep Sea King. While he is blinded, Genos pummels him down with a kick, and continues with his Machine Gun Blows. Deep Sea King remarks how Genos likes combo attacks. As soon as they crash down, the smoke clears and reveals the two fighting to a standstill. The civilians then retreat from the ensuing battle. While they are running away, a little girl shouts to Genos that she believes he can win. Upon hearing this, an annoyed Deep Sea King spits acid at the child, stating that brats should keep quiet and melt away. Left with no other choice, Genos throws his body into the path of the acid spit, saving the little girl but damaging his body greatly. Taking advantage of this, the Deep Sea King grabs Genos by the head and throws him into a nearby wall, following-up with a devastating punch that sends Genos through the wall and out onto the street. With most of his upper body melted off, Genos is defenseless. The Deep Sea King laughs, then grabs the decrepit Genos and throws him across the stadium and into the street. Standing victorious, the Deep Sea King congratulates Genos for giving him a few scratches, but states they have already healed. He also mocks Genos for throwing the battle to protect a little girl. But just as he's about to deal the final blow, the battle is interrupted by Mumen Rider.

Aftermath
Genos is extremely damaged and immobilized, and when Saitama later arrives at the scene, he asks Genos if he is alive, showing the genuine connections he has made with the teenage cyborg.