Yakutatazu Skill [Login Bonus] de Suterareta Reijou ga, Hontou no Shiawase wo Tsukamu made

Joanna is devastated when her younger sister steals her fiancé. But then, a new engagement proposal arrives: Vincent from the Linehan Marquis family. With her previously useless "login bonus" skill blossoming, and receiving doting affection from the handsome future Marquis Vincent and his family—the unfortunate young lady Joanna finds true happiness in this sweet fantasy!

(Source: Futabasha, translated)