Miss Huge Rack and Her Coworker, Mr. Well-Endowed -Getting It On At The Office-

Hotaru Shina is an office worker with a powerful libido and imagination to boot. She spends her nights alone, pleasuring herself with adult toys. One day, while she's working overtime, she realizes she brought one of her toys to the office! To make matters even worse, Ryo, the top sales rep and someone she looks up to, walks in on her holding it! She thinks he'll be repulsed, but the usually sweet Ryo reveals his own dirty appetite. He pounds her hard with something way bigger than she's used to. She'll never be able to go back to satisfying herself again...!!!
They've got great physical chemistry!! This is a secret office romance about two people who were made for each other.

(Source: Renta!)

Note: Chapter count includes a bonus chapter.