Kenja wa Nemuru: Shinjou Mimei no Houseki Jikenbo

Miharu is a very good girl, plagued by very bad luck! Her mother has died, leaving her only a single ring to remember her by, and her father's gone bankrupt – leaving her with all of his debts! Intending to sell the ring to pay off those debts and start a new life, Miharu crosses paths with Rintaro, a "jewelry expert" with more facets than the sharpest diamond. Alchemy, mysteries and gems both cursed and stolen all come together in this glittering series of comedy, horror and suspense!

(Source: Go! Comi)