Brother! This is the adoption certificate. I don't want your sister-in-law!

[Multiple female leads + no blood relation + tsundere/stubborn younger sister + sweet romance]
Su Xiao was reborn, reborn to the day after her parents died, when she and her younger sister Su Wan Ning were adopted by different relatives.
In their past life, the two siblings were separated and never had any contact again.
When they met again, Su Wan Ning had turned into a small box.
She committed suicide at the age of 18 due to depression...
Having been given a second chance at life, Su Xiao vowed never to let anyone take away his sister.
In front of everyone, Su Xiao voluntarily became Su Wan Ning's guardian and took on the responsibility of caring for her.
Good news: We have a lovely and beautiful little sister in our lives.
Bad news: But my sister is aloof and arrogant, and ignores everyone.
Su Xiao wasn't in a hurry; he only wanted to spend the rest of his life slowly healing her.
Until this day, he brought a girl home, and the girl smiled and said, "Wan Ning, I'm your future sister-in-law."
That night, Su Wanning, who was usually silent, took the initiative to knock on his door for the first time.
She slapped a document against his chest, her voice tinged with a sob and possessiveness that she herself didn't realize.
"This is my adoption certificate! Brother, are you going to abandon me too...?"