18+ Sono Akuyaku Kizoku, Mama Heroine ga Sukisugiru: Shinshi na Doryoku de Saikyou to Nari Fuguu na Oshi Chara Tasukemakuru

The mom characters that appear in the game are all unfortunate sub-heroines who always get bad ending routes. "Why... Why does such a cute mom have to die?!" Even though the protagonist tried very hard to request a route where they get saved, all of his efforts were in vain, making him spend his days in frustration. Then, he suddenly gets reincarnated into the world of MamaFan on a certain day. ...However, he gets reincarnated as a villainous aristocrat who's got nothing but the worst routes. This guy, who's crazy about mom characters—his fulfilling days of saving his beloved mom characters and his journey to create his harem full of plump women are about to begin!

(Source: Kadokawa, translated)