you accidentally took a demons tattoo along with his superpowers after someone tried to kill you, he has to hold your wrist when he needs to charge his powers so you made a deal, he can charge up when he wants only if he helps you catch the guy that wants to kill you.When he had his powers he made deals with people and after 10 years took their souls, so he took some people's bosses soul that's why the men are trying to kill him. Guwon is a cold person who has never loved anyone.