Warning: Spoilers ahead.
This season picks up soon after where season 1 ended. The Shield Hero Naofumi Iwatani was rewarded Raphtalia’s old hometown land, Lurolona Village, for all he’s done for the Melromarc kingdom.
Naofumi has many allies now and many people who trust him. The people of his new lordship are preparing for the next Wave of Catastrophe.
Elrasla Ragralock AKA Granny is training Rishia Ivyred and Keel, when suddenly a bunch of creepy bats arrive and attack the village. But Raphtalia and Filo make quick work of them.
Queen Mirellia calls Naofumi, along with the other three Cardinal Heroes - Ren Amaki, Motoyasu Kitamura and Itsuki Kawasumi - to meet and discuss the problem. Somehow, a legendary creature called the Spirit Tortoise has revived. The weird monsters like the bats are the tortoise’s underlings.
The other three heroes quickly say they’re only supposed to take care of the Waves of Calamity. Not this tortoise, so they decline from helping. Seems they’re still jerks.
But Naofumi stays to help. The creature has already left death and destruction in its path. It is heading through Melromarc and even Naofumi’s territory soon.
To help fight, Raphtalia gets the idea of having Rishia become one of Naofumi’s slaves, so she can level up and stuff. She agrees to the idea really easily.
Later, while traveling, Filo is able to speak telepathically with Fitoria. Fitoria checks in to see if Naofumi is able to work together with the other three heroes.
Some time after this, more tortoise minion monsters attack people. Naofumi’s party is able to save them. He has to unleash the Wrath Shield, but he isn’t damaged much by this.
A mysterious woman appears in front of Naofumi’s party asking to be killed. Then she disappears.
Then she appears again, at a meeting of generals who have formed an alliance to stop the Spirit Tortoise. Her name is Ost Hourai. She’s been disguising herself as a human, but she’s actually the Spirit Tortoise’s familiar.
Anyways, she wants to help the humans stop Spirit Tortoise. Seems some mysterious figure woke up the Tortoise even though it wasn’t supposed to be. The creature’s actual purpose is to gather human souls to defeat the Waves if the Heroes fail. But it’s pretty much gone wild now.
The generals argue about how to fight the monster. But finally listen under Naofumi’s command.
Finally they prepare for their assault. And the Spirit Tortoise arrives!