I'm pretty sure the story Phishy is referring to is "Copping A Feel" by Keva
www.inuyasha-fanfiction.com/viewstory.php?sid=372
Copping A Feel by Keva
Summary: Sess has an uncharacteristic compulsion, Inu is PMSing, Muso is on the loose, Naraku is a perv, and Kagome is going to kill them all… Starting with one hentai demon lord. Humor, M/F and extreme hentai behavior!
Rated: NC-17
However, I am POSITIVE this would be rated MA here on Dokuga, so please no YIM'S!
I had difficulty getting into the story with the link, you may have to go to the homepage and then search "Keva" then page down to find "Copping A Feel".
The story has 8 chapters, and the part Phishy is talking about is in Chapter 7 and Chapter 8. Unfortunately it is incomplete, and I cannot find it anywhere else.