The Story goes a little like this:

Warring States Era.

Inuyasha Gang + Sesshomaru trapped in a sealed room with (perfume/poison?) that causes them to mostly sucumb to the UST present in the canon storyline. They escape, but I believe there are consequences.

In later chapters Sesshomaru seeks Kagome's assitance obtaining a special potion to extend Rin's life specifically because of her responses while in the sealed room.

Any help would be appreciated. Thank you.

- SunLynx

Maybe it's Absolution by Demonlordlover2?
dokuga.com/spark/story/7398/1
Summary: Acceptance does not give absolution. So said the gods. If he wanted to retrieve his honor, he would need to seek forgiveness from the woman for stealing that which he had no right to take. Given her loving nature, Kagome finds it impossible not to forgive. The question is, can Sesshoumaru forgive himself?

Awesome! You found it. I think perhaps the length led my adled mind to believe that it was a chaptered story, and it's likely I passed this story over as the summary didn't sound much like what I was looking for at all.

Thank you so much for looking for me.

- SunLynx