Melromarc brings a large fleet to fight the Wave out at sea. While the queen takes charge and leads the operation well, the other three heroes prove useless yet again, leaving Naofumi to do it all alone. Later, he gets help from L'Arc and Therese to fend off the monsters, but then.
Tropes for this episode include:
- Anti-Villain: L'Arc reveals that he is a cardinal hero from another world with its own waves of catastrophe. If they don't kill Naofumi and the three heroes and allow the Waves to destroy this world, their world will be destroyed instead.
- Armor-Piercing Attack: L'Arc's scythe is able to cause backlash proportionate to his opponent's defensive stats, making him the perfect counter to Naofumi's attack-sponge speciality.
- Chekhov's Gun: The alchoholic fruit from before is weaponized to pacify the sea-monsters, making them easier to pick off.
- The "Hate Reaction" spell that Naofumi used on the penguin monsters in the last episode are used here on one of the whale monsters.
- Fish People: A group of gill-men invade the ships, one of which nearly swimming off with Melty.
- Noble Demon: Much like Glass, while L'Arc and Therese were sent there to kill Naofumi, they prefer to fight fair.
- "The Reason You Suck" Speech: When the three heroes try to claim some of the dropped items that L'Arc and Naofumi killed, saying that they belong to "all of the heroes", L'Arc can't help but laugh at how incompetent they are.
- Sea Monster: All of the monsters coming from the wave are aquatic in nature.
- Skewed Priorities: Averted. While L'Arc and Therese came to kill Naofumi, they are willing to work with him to kill the monsters in the wave first.