Based on the game by WendyBell. A beautiful girl’s body is inhabited by a tentacle monster that forces her to attack other cute girls.

There once was a demon Astaroth who invaded the human kingdom, plunging the world into war. However, he was finally suppressed by a group of heroes who took his powers and sealed him deep underground. Two hundred years later, there were rumors that the seal was broken due to the recent shifts in the Earth’s crust and that the demon had been revived. Many confident adventurers descended on Astaroth’s underground labyrinth with the intention of defeating him and becoming famous. Little did they know that he had set out a trap for them…