MTL - The Lady in the General’s Arms is a Bigshot in Mystic Arts - Chapter 16 : Your fiancée is not a good match

In a post-apocalyptic fantasy world layered into multiple realms, humanity faces extinction due to their endangerment of the main realm. Forced to merge all realms back into one, a deity grants humans a leveling system to empower them, lest they become extinct when facing the mythical creatures. Noah, our protagonist, embraces the role of a monster tamer, trading his humanity for strength and eventually transforming into a monster himself. As Noah struggles with his evolving identity, he must navigate a world where the line between human and monster becomes increasingly blurred.

One day I got a younger sister.Only I know her true identity.

His name is Gao Yang (高阳), not a lamb (羔羊: gāo yáng), okay! If a gentle sheep gets upset, it will bite. Believe it or not!

Gao Yang a sheep in wolf’s clothes: Don’t come again! Otherwise, I will be rude!
Qin Shaoyan: Oh? Why not?
Gao Yang: I… I… won’t cook for you!
Qin Shaoyan: It doesn’t matter, just eat you.
Gao Xun: What if Dad dies after being eaten by Father? Waiting online, urgent!

- Description from Novelupdates

Upon meeting the girl who would become her adopted younger sister, the duke’s daughter Christina regained memories of her previous life. Through those memories, she learned that her new sister, Mishuli, was the heroine of a certain story. And though the story depicted a Christina who abused her sister, the real Christina turned into a siscon who spoiled Mishuli to no end.