Hanayome ni Haizoku Saremashita

"I'll promote you to the CEO's wife." A secret marriage to a handsome, egotistical CEO!? Suzuka is an ordinary office lady with no redeeming qualities. She is always asked to do odd jobs, but one day, by chance, she closes a big deal and receives an order from the CEO to be promoted! She is assigned to... the position of "CEO's wife"! "I'll teach you this too," he says, even giving the inexperienced Suzuka some sexual instruction!? What will become of this fake marriage...?!

(Source: Flower Comics, translated)