Sounds like it could have been Kryptonite by Danyealle-sama, but she took it down to adapt it into an actual book.

Don't remember who wrote this, just that it's fairly old and is Rated MA. Set Post-Canon, basically Inuyasha is abusing Kagome, specifically including that his idea of smuts is using a certain body part as a scratching post. Sesshomaru due to pack obligations rescues her from him and takes her (and I think Shippo?) into his custody where he sets about righting the wrongs. In a later scene Inuyasha is sitting in a tree eavesdropping on Sesshomaru and Kagome together, taking notes while planning on how to punish her later after he kidnaps her back, which I remember does happen at one point.