Xxxholic - CLAMP

Kimihiro Watanuki is the indentured servant of Yko, the beautiful but completely unpredictable Space-Time Witch. He must work at her bizarre wish-granting shop until he can pay off his own wish: to be free of the spirits that haunt him. Yko's latest customer is a rain spirit who wants Kimihiro dispatched on a rescue mission. Little does Kimihiro know that this mission will take him to death's door.

And that's not his only problem: a cute spirit has given him a Valentine's Day present, which means he's obligated by Japanese custom to return the favour. What do you get a girl who may not even exist in this world?