When a person who under goes extreme depression/anxiety, loses control, a person will become a demon consumed by darkness. Luckily there are those devoted to hunting those demons.
Boy meets monster while taking shortcut home from school, is rescued by a girl with a gun. Monster gets away. Later on, girl makes contract with boy and uses his soul energy to make a big gun and kill the monster.

The office of the Time Eliminator offers a unique service, the ability to eliminate an event that happened in the past. Rex, the man with the power to travel through time, may look young, but he's a professional. He goes back in time well-prepared, with various gadgets and even an earpiece for communication with his support in the present. While Rex typically takes on cases for profit, he's also particularly looking for ones that might give him a chance to obtain a magical "Babylon Item". The first case of the series is from the last remaining descendant of Fred Abberline, who was one of the detectives who failed to solve the notorious Jack the Ripper murders. Ever since then, the Abberline family has been cursed. Could the curse be the sign of someone in the past using a Babylon Item?! It's up to Rex to go back in time to the Jack the Ripper incidents and find a way to remove the curse from the Abberline family!