Mistelteen no Mahou

Mistelteen no Mahou summary:

Karasawa Makoto just found out that she wasn't her parents' daughter, but their niece. They give her the only thing her real parents left for her. After receiving it, she goes into an elevator and drops it near a foreigner. He then tells her that the item her parents left her allows her to rule the world. The foreigner's partner then snatches the item and leaves. (manga traders)