Help me find this manga

Guys I read this manga years ago but then I lost it, maybe somebody can help? Here's the plot:

So a woman is a very good worker, always wears oants and even during sex she will answer her boss' calles. That has ruined a lot of her relationships, she is often compared to how a guy acts when working and (maybe I am not sure about this one) has a nickname related to this, like metal something? Idk. She has long hair, blonde. They get a new guy at work and for some reason they start a game-like bet, they have to please each other sexually and whoever pleases the other more wins. For example, the guy covers the girls eye and does cunni, she even screams because if the pleasure, later when she blows him the guy enjoys but doesn't scream because of the pleasure which makes the girl bummed out and makes her feel she lost. It's not Manhwa, it's definitely japanese manga.

This is all I remember, I really really hope somebody knows which manga I am talking about, I've been searching for it for years.