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 in return for his help preserving his beloved sister's 'memories', gets all the troublesome jobs pushed on to him.

The shop deals in human emotions. Any forbidden or irrepressible emotion that is tormenting the customers 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...

From Fantasyshrine:

For the sake of his little patient, Resident Doctor Yashiro Takashi agreed to a bet with the beautiful doll maker, Kuze Shinobu, who claimed to be his “destined one”. Unaware of their intertwined fate, Takashi had bonded himself with Shinobu in a spirit marriage.