If you liked the Isuca manga, the Anime-Planet community thinks you'd like:
If you take Isuca cut down most of it's ecchi and replace the characters with improved ones, you'll get Kandachime. If you found those two parts unsatisfying in Isuca, you might as well give Kandachime a try.
If you took a liking to the resident Nekomata in Isuca, you might want to give Koneko Pancake a try. It has lots of cat-girls, at least one of them is as affectionate towards the male lead as previously mentioned Nekomata towards her "master", you won't find any real tsunderes there and last but not least, the content is much more dere-dere driven than fanservice driven.
Yuuto Amakawa has had a tough life. Seven years ago, both of his parents were tragically killed in a car accident, leaving him without a single living relative. His friend Rinko Kuzaki has taken care of him every since. Yuuto's sixteenth birthday has arrived, but instead of a birthday gift of a normal life he meets Himari, a catgirl samurai who swears to protect him. Within weeks Yuuto's life is thrown into chaos as his family's dark past comes to light. With demons appearing around him, Rinko and Himari fighting for his attention and a sinister plot beginning to surface, can Yuuto live the normal, safe life he wants so badly?
Those series are awfully similar. Both revolve around some normal guy who suddenly finds himself involved with a number of exorcist girls and some youkai (namely a female cat one). Both series go too far with ecchi, but Omamori Himari is the one more guilty of that, On the other hand the characters from Isuca are a considerable improvement over those from Omamori Himari (that doesn't mean they're any good and one can't forget that the female lead from Isuca is a horrible tsundere).
The similarity is there, but I really don't want to go into details here. Both series give a similar vibe, but the story and characters are notably better in Sekirei. If you read one and you are desperately searching for a similar series, the other might prove itself to be just that.
If you liked Musubi from Sekirei or the nekomata from Isuca you'll probably going to like the other character as well.