Similar themes of social hierarchy and similar situations. In both, the girl is impoverished and ends up being "bought" as a wife for a noble who really wants nothing to do with her at first.
In the year 1580 in feudal Japan, Fifteen-year-old Usagi is a klutz of a ninja who can't seem to complete her training. As she's unfit to be a ninja her great grandfather sends Usagi to Segachi on a very special mission: to marry the skilled ninja Hanzo Hattori and bear his child! However, there's a problem: Hanzo has no desire to be married. Usagi is allowed to stay with Hanzo for one year in order to complete her training, during which she tries her hardest to catch his eye. But lovely rivals such as Yuri and the Princess Sara, and love triangles with childhood friends and others stand in the way of true romance. Will Usagi ever end up with her beloved Hanzo?
Considering it's written by the same person, it is not surprising that the two would have coinciding themes. Both have the semi-forbidden love feel, the barrier of the heart (if you will). Both main characters have a clumsy air about them and both have some sort of creeper hanging on to a past relationship with said heroine and wishing for things that could have been. I must say however, the creeper in HdBwF is much more excessive *gets chill*. Liked him at first but...ANYWAY.
Both of these series follow the development of a common girl who is suddenly lifted to the lap of luxury. The transformation is difficult for both of the heroines, and enemies are often disguised as friends, but neither one is easily broken. If you like rags to riches stories, either of these is a good choice.