Shitaiyaku Reijou ni Tensei Shitara Kuromaku Ouji no Shuuchakusare Chaimashita

Meredy, a mob character who is killed at the beginning of a girls' game, has been reincarnated as the "Corpse Lady." Her goal is to prevent the encounter between the game's mastermind, the First Prince Jake, and the "Book of Demon Summoning," which holds the key to avoiding the bad ending! Meredy uses her memories from before her reincarnation to get in Jake's way, but for some reason, Jake asks her, "Would you like to make a deal with me?" and nominates her as his "playmate" instead! Set in the school of a girls' game, a love romance begins, featuring a chase between a mob lady and a yandere mastermind prince!

(Source: Kadokawa, translated)