The first lemon is in a cave, Kagome wanders away from their sleeping area after Sesshoumaru told her not to and found a spring to take a bath. Certain actions on her part lead to a lemon. Later she mates him and again lemon and there is a building which glows and flowers bloom. It's a chapter story if I remember correctly.

It's in the Blood by sarhea rated MA

Didn't think I'd find it. I looked everywhere and then remembered that I have a crap ton of labeled bookmarks in firefox.