Yuuko is a mysterious woman who owns a shop of equally mysterious nature. Her business works on following conditions: to get a wish fulfilled her clients have to pay with adequate reciprocation. That is also how she made Watanuki into her personal "servant".
She loves Sake, which she drinks as if it was water. And she loves to joke around and tease Watanuki. Her laid back and joyful nature is very versatile in situations that require her to be serious, then her serious side takes over.