Arata Kasuga, a high school student, is being targeted by a girl with humongous boobs. In exchange for his life, Lilith says that she can erase his memories, but he chooses the third option. As a result, he ends up at a magic school, but why is there a naked girl in the men's bath?

In order to become a mage, you need a research theme which archives one of the seven deadly sins. While thinking about what his theme will be, Arata and 3 others are locked in a barrier, with no exit to be found. But then Lilith and the others find themselves needing to use the restroom... Good luck, girls!

It's summer. The gang's on a southern island, and there's cute girls in swimsuits abound. Arata's cooking yakisoba for some reason, but these things happen. The quartermaster is repairing the school that Arata destroyed in his collapse phenomenon. The girls enjoy a mixed-gender bath, and the demon lord candidate decides on a theme--control.

A power leaks from underneath the school, Arata and the gang head down into the labyrinth to protect the school from the collapse phenomenon.

The girls are running in their exercise outfits, with the boobs swaying to and fro. Arata's heart races. Everyone's having great time, and then a ghost appears in the library. Arata and the gang go to check it out, and are forcefully transported to the "Eternal Library". There they find the lost Trinity Seven!

Liese, the last Trinity Seven, appears in the Eternal Library bearing a demon lord seal, making her a demon lord candidate, as well. She tries to entice Arata to join the evil mage side to help save Hijiri, and kisses Arata while he's unsure what to do. Arata has his magic stolen from him, and Liese decides to attack the school.

Arata is appointed to be the second in charge for the censorship committee. The whole gang is transported to the destroyed Royal Liber Magic Academy, and there he finds his long lost cousin, but...

Arata and the others appear in a world floating in a rift in the sea of parallel dimensions. Monsters attack. The legendary grimoire, "Fragments of the Iliad" challenges them to a fight. An evil power awakes in Arata due to his anger when the Astil Codex are sealed...

The ultimate demon lord, Astral Trinity, shows up in the form of Arata with a grotesque new appearance. Hijiri appears as well, and the others discover that she is a high-level mage whose goal is to kill Arata and destroy the school.

Lugh attacks the school while Arata and Mira are being held far away. Yui evacuates everyone in the school into her dream to protect them, and Levi sets out to fight alone. But Lugh is a demon lord candidate who has obtained a demon lord element.

It's the last episode, and Hijiri and Arata have their final showdown. Lugh joins in the fight, along with the Trinity Seven--Lilith, Levi, Arin, Mira, Akio, Yui, and Liese. Why is she attacking Arata? And what secret does Arata hold?