The "Demon World" is a world where there are many demon kings.
The Demon Realm is small in comparison to the number of Demon Kings and Demon Tribes that live there, and it was only 100 years ago that the Demon Realm was a warring world where Demon Kings fought each other for territory.
The situation in the Demon World changed drastically with the establishment of magic technology to transfer to another world.
As transfer magic spread, demon kings began to invade other worlds. The hero, a demon king, is one of them.
However, the protagonist was so weak that he could be said to be the weakest of all the Demon Kings. Furthermore, the world he was invading had inhabitants with high fighting ability called magical girls, and the magical girls beat him back, making it difficult for the protagonist to invade.
The main character was still able to continue his invasion because of his ability to revive himself even after death.
One day, he invaded the magical girl's world as usual, was beaten as usual, and revived as usual. However, unlike usual, the protagonist's memory is gone... (Continue to the main story)