Shoto Todoroki vs. Leviathan

Katsuki Bakugo vs. Serpenters is the battle between Shoto against Humarise warrior Leviathan.

Prologue
After investigating the microSD they found in the briefcase, Shoto, along with Deku, Bakugo, and Rody, manage to locate Humarise's main base on an island near Otheon, and they immediately head there by plane to stop the Trigger Bombs after Flect Turn publicly broadcasts to the world that they will detonate them in two hours in different cities around the world.

Once there, the three U.A. students face fierce resistance at the entrance, though Shoto and Deku fight their way inside, while Bakugo stays behind to deal with the last few defenders. As they advance through the corridors, self-defense systems attack them while more soldiers come out to stop them. Shoto tells Deku to continue while he stays behind to hold off the incoming reinforcements. A squad of Humarise followers attack Shoto with their guns, but he defeats all of them at once with his Super Move Flashfreeze Heatwave. However, before he's about to follow Deku’s path, Leviathan appears, ready to finish him off.

Battle
Seeing the gigantic enemy charging towards him, Shoto attacks him with a flame to stop him, but the behemoth undeterred runs through the fiery attack and tries to crush him with one of his huge hands. Shoto manages to avoid the blow and tries to take shelter in another room, blocking the door with ice, realizing that the fire does not seem to affect this new threat.

Using his Helical Scythe Quirk, Leviathan destroys the block of ice to chase after Shoto, who realizes that his foe is induced with Trigger, that not only makes him and his Quirk more powerful, but also makes him unaware of the pain.

Leviatan attacks his prey using the semi-liquid appendages on his hands, forcing Shoto to use his ice powers in an attempt to avoid being hit by one of the red tendrils. One of them shatters the block of ice he is on, leaving him defenseless against Leviatan, who grabs and stomps him against the ground, falling both to the lower level, where there is an underground river.

Leviathan falls into the water while Shoto manages to grab onto the edge, but as he's about to climb, the Humarise soldier uses his Quirk to generate a watery column that makes Shoto fall into the river, and once there, he creates semi-liquid tendrils to hold Shoto underwater until he drowns. Every time Shoto manages to undo the tendrils by freezing them, Leviathan quickly generates new ones, preventing him from escaping.

Shoto is about to lose consciousness due to lack of air, but fortunately, he notices that the underground river leads them to a waterfall outside, giving him the chance to escape Leviathan's grasp. Shoto freezes the tendrils again, but this time he doesn't undo them, but they hold on long enough until the two begin to fall down the waterfall, at which point he breaks free using his fire.

With no water to use, Leviathan attacks him with all of his red appendages, but Shoto fuses his ice at maximum power to freeze the tendrils, Leviathan himself, and the entire waterfall. Despite being trapped in the ice, the giant manages to free his head using its appendages, and tries to attack Shoto with them. After dodging the tendrils, Shoto uses his fire to generate a powerful Flashfreeze Heatwave, which causes a huge explosion.

Despite this, the villain not only manages to withstand the attack but also uses his Helical Scythe Quirk to control the flames of the explosion, creating a gigantic version of himself that "swallows" Shoto, trying to burn him under the extreme heat of fire. Enduring the temperatures as best he can, Shoto concentrates all the power of his flames at their highest possible point, attacking Leviathan with his Flashfire Fist: Jet Kindling, burning the villain up from the inside.

With the villain defeated, they both fall over the waterfall. Shoto's last thought before losing consciousness is to wish that Deku can stop Humarise.

Aftermath
Shoto is left unconscious for the rest of the battle, but just as he had wished, Deku, with his strength of will and the help of Rody, manages to defeat Flect Turn and stop the countdown of the Trigger Bombs, preventing a mass genocide on a global scale. Law enforcement and various heroes arrive at Humarise's secret base and arrest all of its members, including Leviathan, as well as rescuing the boys and taking them to a hospital to treat their injuries and wounds. They remain in place until they fully recover and are able to return to their homes.