Jack the Ripper is a little girl! In order to save his girlfriend, Colin followed an order and bombed a bus. Chased by the police to a dead end, he decided to commit suicide when one little girl showed up and saved him. Who are you? I’m Jack the Ripper, and I will be your spirit servant.
But why would the demon lord summon him? Yeah bcz demon lord was bored wants to fight against a new toy or he was fed up of his immortality and wants to die now.