I like how she's come think of herself as a vital tether to normalcy in Yuuto's life. You're right, there's character development in Omamori Himari. It's not shoved in your face though, it's subtle. I think that Omamori Himari would come off as just another Harem to a lot of people, but it's much better than that. And there's pantsu.
No matter where you go, there you are.