Hiiragi Seichi is an unattractive high schooler who gets bullied; one day, a mysterious voice suddenly rings out over the school's PA system and sends them all to another world.

After Seiichi defeats a gorilla-like monster, a Kaiser Kong, she proposes to him. The gorilla named Saria starts her new life together with Seiichi. While she is kind, innocent, and forthright, he still plans his escape from her since she’s a gorilla. After wandering into a cavern he finds a skull putting off a strange aura - the dark lord Xeanos. Seiichi begins to battle Xeanos, a creature as strong as most final bosses! However, disaster befalls Seiichi and Saria leaps in before him!

Saria had lost her life in battle, but after eating the Fruit of Evolution, she revives as a human.

Seiichi and Saria train under Artoria to become adventurers; they are teleported into a dungeon by a demon's trap.

Seiichi rescues Artoria with her on the verge of death; he faces the Black Dragon God.

Seiichi's attempts to cheer up Artoria; Seiichi and Saria pass their tests and successfully join the adventurer's guild.