This film is set in an alternative world where high class families have supernatural abilities and warriors fight against the "grotesques", evil spirits that can possess the bodies of humans. A young girl from one of these families is born without any supernatural gifts and is neglected and abused as a result. She is married off to the stern captain of a troop of "anti-grotesques" who is actually good-hearted and she receives kindness for the first time in her life and blooms as a result. Neither is aware that the young woman is the progeny of a family with unique abilities craved by others seeking power and influence.
I came to this movie with absolutely no knowledge of the manga and anime upon which it is based. I think they do a good job in laying out the nature of the world in which it takes place. It's interesting to see old fashioned clothes and modern conveniences (like cars) side by side in a fantasy context. The two main actors are very good and the film works because you believe in them and their relationship. It's an odd title (my happy marriage) but apt in that the affection between Kudo and Mia is really the core of the story and what drives the plot forward. By necessity, the action is a bit rushed (though I didn't feel it the first time through). My only criticism is that the climax of the movies is confusing (but still effective) as the screenplay doesn't have time to help us understand exactly what's happening and why. I think fans of the anime might find it a little disappointing but I found it an enjoyable way to spend a couple of hours.