Risou no Seijo? Zannen, Nise Seijo deshita! Kuso of the Year to Yobareta Akuyaku ni Tensei shitan da ga

After yet another late night of playing his favorite dating sim, Fudou Niito—a self-proclaimed lazy NEET—suddenly wakes up to find himself inside the game! Stranger still, he hasn't been reincarnated as the main character, Verner, or as his beloved waifu, Eterna... Instead, he's Ellize, the absolutely awful fake saint who stole Eterna's rightful place and made her life a living hell! And so, Niito now has one goal: change the story to ensure the game's tragic heroine finally gets the happy ending she deserves! To do that, he'll have to play matchmaker for Verner and Eterna while also boosting the saint's popularity! Can this imposter scheme his way into a happy future for his favorite character?

(Source: J-Novel Club)