A keykeeper and the watcher of the two worlds, Karen is a man who has lived way longer than what should be humanly possible. He is a fixer of all things that cannot be fixed, from hopelessly broken hearts to objects that simply couldn't be fixed with anything anymore. Although Karen leads a rather lonely life, he doesn't feel himself particularly lonely. After all, he is always busy with the affairs of the demon world and is often helping out those in trouble.

Because Karen was originally a normal human, he was made sensitive to spirit world through hallucinogens he was forced to smoke until his mind and senses could open up to things that usually cannot be seen. Although Karen doesn't have to smoke anymore, once in a while the old habit kicks in. However, he usually smokes only when he is stressed or when he is paying his respects to his now deceased mentor. Smoking what his mentor made him smoke as a student is equal for him to having incenses.