Hi all, been looking for this for a while but no luck :(
The guy is some sort of sex trainer who train girls for his clients, all according to their tastes.
The manga showed a couple of girls being trained, I think two of them being sisters or something like that.
He went in to this kind of stuff because he wanted to train his own childhood friend.
Turns out his assistant sent his childhood friend to another sex trainer, and revealed this info after the dude fulfilled her request to be trained like the other girls.
Also I think the assistance looks a bit like Tokisaki Kurumi
That's all I remember
Any help appreciated!