Merian is the headquarters of the booming business world of "Mesu Onii-san" or "Bitch/Female Men". One of the persons employed at its lounge is Reo, a Mesu Onii-san with the temperament of a mad dog. One day, he messed up when attending to a customer of Mikame's, a platinum-ranked Mesu Onii-san there. Reo later went to drink his frustration away and ended up spending the night with Yanagi, the bartender who accompanied him then.

When he woke up the next morning, something he noticed on Yanagi's ring finger made him wonder if this was just a one night stand. This is the start of the spin-off of the popular series Zenmeren horny BAAAD!!