Koutei Heika no Senzoku Shisho Hime

Kanon realizes that she has been reborn as the villainess of a game. On her 18th birthday, her fiancé, who had chosen her half-sister to be his fiancée instead, breaks off his engagement with Kanon. Obediently accepting this decision, Kanon heads for the imperial capital. Her goal was to escape the worst possible outcome and live a peaceful life as a librarian, but she ended up signing a love contract with the emperor, one of the love interests of the game?! My fiancé, my step-brother, and my boss are all love interests of the game, and I'm just the heroine's stepping stone?! Being the villainess of an opportunistic game is no joke! A villainess' work x contract love fantasy!

(Source: Ichijinsha, translated)