Ariel, who likes to play pranks, was thrown out by his parents to wander, and then he was taken in by a system that was very good at playing tricks. He could also go to different spaces to become a monster.
The full name of the system is the Horror Game Survival System, nicknamed "Youyou", and his friend is the alien creature Ailere. Recently, he took in Alaire who was kicked out of his home, and then the two unknown objects became a monster together.