From Shoujo Crusade:

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?!

Extra story Sweet Guardian:
Kasuga Yuuki had always been in love with Himuro Makoto. One day she decided to confess to him and ended up rejected. On the same day she fell asleep on a supplementary class and ended up staying late at school. To her happiness, she found out that Himuro-kun was also still at school, but somehow he had a gun?! Moreover he tried to kill their school Chairman and admitted he is a hitman?! And later she ended up going out with him!? Is this all a dream?!