Kaitou Wa Koyoi Mo Hanataba Wo. - Namida No Jewel summary:

The perfect combination of a mysterious young lady thief and an intelligent butler!"Phantom thief Lady Black" is a thief who wears black clothes like mourning dress and only targets jewelry. Her true identity is Aria, the daughter of a jeweler with a sad past. One night, after she obtains the jewel she's been looking for, a mysterious man appears in front of her...?!