Kiyoku Tadashiku Iyarashiku: Majime OL no Bitch Sengen

Sick of being the good girl, Misono Funaki, an office lady in her twenties, decides to start sleeping around. She was supposed to have a one-night stand with a random guy she picked up, but for some reason, they end up as friends-with-benefits. However, a week later, he shows up at her workplace as the new section chief in the same department, and she is not happy about it. The heroine tries her best to play the role of a bitch in this heart-warming office love story. (Source: Mitsuyume Bunko, translated)