I think your looking for Close Encounters Of The Fluffy Kind by KogasAngel
It is the night of the blood moon, and Kagome had found out that she is cursed. During this particular moon, she goes into a very powerful heat, and will allow her to produce full blooded youkai should the male chose to pup her. Sesshomaru, still sore about losing the tetsaiga, finds Kagome in a small cave and decides to confront her and take his revenge. He gets more than he bargained for.
www.dokuga.com/fanfiction/story/2580/1
Rated MA