Strum My Lost Voice

"Official Sex" In the corporate underworld lies the Secretary Association, an organization that holds lowlife people as paws known as "secretaries". These secretaries fight in sex battles with corporate funds and assets wagered. Amidst all of this, there is one ranked number one: Ryuga. After his most recent victory and payout, Ryuga was enjoying a walk and a cigarette when suddenly he bumped into some hot shot in a suit. After some arguing and money changing hands the two hoped to never meet each other again... until the following day when Ryuga learns his new patron is the very same man, CEO of a big company. Onizuka is a ruthless businessman in the corporate world, and although he's not fond of the fact that he has to get his hands dirty with the Secretary Association, he's willing to do whatever it takes. "Are you sure you can keep winning?" Those words set off Ryuga to prove himself to Onizuka, but it seems Onizuka is different from anyone else up until this point...?!

(Source: MangaPlaza)

Notes:
- Chapters 7 to 9 were split into two parts in the original serialization and later combined in the volume release.
- Includes three extra chapters.