Transmigrated Into a Revenge Novel as a Cannon Fodder Female Supporting Character

After regaining her memories from her previous life, Jiang Muyun realizes she's actually transmigrated into a revenge novel about punishing scumbags, becoming the heroine's senior sister. Her junior sister is beautiful, sweet-voiced, kind, innocent, and adorable. She's everyone's cherished first love. But that cherished first love died three hundred years ago, for Jiang Muyun's sake. According to the original plot, her junior sister will soon return under a secret identity, having turned evil, and embark on a series of brutal acts of revenge against everyone who once hurt her. But reality takes a strange turn: the person returns, only now she's a man. Jiang Muyun: "...???!!!" Junior sister! What on earth happened to you over the last three hundred years?! * [Things to Know] 1. The junior sister is a cross-dressing man; 2. This is not a traditional cultivation novel; 3. If you only want pure romance, don't read this. Don't waste your time; 4. I'll add more if I think of anything; Theme: Romance