It’s Having Fallen Off (rated M on fanfiction.net) by LeSinner and adopted by CammiiLyin.
www.fanfiction.net/s/8882990/1/Having-Fallen-Off
It’s also MA on this site.

The summary here was posted in a forum in dokuga and this is exactly what I am looking for

"Hmm, there is also a canon one where Kagome is the heir of a influential yakuza group and finds (500year-older) Sessh with his powers bound and as a slave (she persuades her uncle and aunt - who are the current heads- to take him). He acts as her right hand, or atendant (or vasal or sth), and is bound to her by the collar. I also know she's a virgin and has a need to 'pop her cherry' because it's bad to have such a weakness in her business. One of her professors is Bankotsu's reincarnation..."




Thank You!