Antasya Rei, a high school in his 4th year woke up in another world, in a body of the so called demon king from the myth.
In order to return to his original world, he almost destroyed the world he was thrown to with his invincible body. And due to an agreement he made with one of the human pillars, he was able to return to his original world. He swore to himself that he'll live an ordinary life like he always wanted and die peacefully from old age.

Will his life be at peace before then though?