Alright. Let me get this out. This is Zero no Tsukaima. The only difference is that the main character is strong from the start and the talking sword is a girl. Everything else, the main heroine, the rest of the harem, the slave thing (UGHH!) and the school setting is the same.
So if you liked Zero no Tsukaima, you'll like this.
But if you're not a "M" kind of person, and you didn't like