Lady's Orders(2008)

Ojousama Gomeirei wo

Kurai Karen is a rich ojou-sama with many suitors. She's in love with her butler, Ishibashi Megumi. Long ago, the two of them made a promise to be together forever. Now that they've grown up, Megumi seems to have forgotten, but Karen hasn't. A forbidden love between master and servant, what will happen to them?!
(from BU)