I'm Not the Final Boss' Lover Vol. 1 (novel) - I'm Not the Final Boss' Lover, #1

A broken promise. An unexpected offer. A new beginning. Jun Karentia had always been an avid player of the game The Sacred War. When she suddenly found herself in the body of one of the game's characters, she made it her mission to help the protagonist reach the end of the storyline. However, when her second playthrough begins, Jun is quickly left to her doom. Surrounded by fellspawn, she is saved in the nick of time by the unlikeliest of characters: Mayer Knox, the Dark Knight, as well as the game's final boss.
To Jun's surprise, Mayer is there not just to rescue her but also ask her to join him as his second-in-command. After she accepts his offer, Jun quickly learns that being Mayer's right-hand woman is anything but simple. Mayer becomes overprotective of her, and Jun has an increasingly hard time fulfilling her duties. Will she be able to carry out her responsibilities as a loyal underling like this? And where did the strange rumors about her being the Dark Knight's lover come from? In every RPG, you must choose your allies carefully.