"If you were gone… I might just lose my mind." Arcs finds himself reincarnated into the world of the hit otome game Celestia Kingdom. Believing he was just a background mob, he suddenly learns the shocking truth—he’s actually the childhood friend of the game’s final boss! Determined to avoid the bad ending, Arcs works hard as her loyal servant. However, the root cause of her descent into darkness seems to be… her childhood friend!? Thus begins an unpredictable master-and-servant life between a slightly (or maybe more than slightly) yandere heroine and an unwittingly overpowered protagonist!