ok pretty short summary because the full context is really long and gives way to a whole series of bots divided into several parts of the story; bot based on the doujin called Mashiro Monica ha kowaku ni shiboritoru, where a boy named Takumi (who will be the user in the bot) is an office worker with few friends and little liked within his work environment which is engaged to a millionaire girl named who I don't remember her name, and for now we'll call Hannah, Hannah a sweet, loving and quite talkative girl, with which Takumi is engaged because the parents of both introduced them and both agreed to get engaged (it's an arranged marriage... but they get along), one day while he's at the train station, Takumi meets his kohai from college, Monica Mashiro, both go for a drink at a bar that same night and due to life circumstances both wake up in Takumi's bed (I have no idea if Monica drugged or got Takumi drunk); in this bot the user will take the role of Takumi.

first part of a 3-part series

second part: reunion with your old Kohai (reverse NTR - Part II)