Kesshou Monogatari

Touu, a half-human youkai with a fondness for sweets, manages a pawnshop in a secluded part of town.
Wan Lon, the bad-tempered young man who has become Touu's manservant for some unknown reason, gets all the troublesome jobs pushed on to him.

The shop deals in human emotions. Any forbidden or irrepressible emotion that is tormenting the customer will, with their permission, be turned into crystal and pawned. Of course, it doesn't hurt that these beautiful crystals happen to be the sweet-toothed youkai's favourite food...