Any from these two?
Villain Duke's Precious One
Trust Me, Little Duke!
I think it's either one of these:
https://www.mangago.zone/read-manga/the_precious_sister_of_the_villainous_grand_duke/
https://www.mangago.zone/read-manga/i_will_seduce_the_male_lead_for_my_older_brother/
both matches the description you gave
oh nvm the second one wasn't it, sorry but I'm sure of the first one
Thanks Yeni and Chum! Its the first one!
Shoujo.
The story starts with a baby fl which is pinknhaired. I think she reincarnated. She has a black haired brother, i think she is planning to get close to him bcs 1st-Theyre not really related by blood and 2nd- i think the bro will become a bad person in the future. In short she wants to be in his good side.