A boy is adopted he protects his new sister parents support him sorry not much to go on
That sort of reminds me of Argon's https://storiesonline.net/s/22004/suddenly-rich-kid except that he was not actually adopted, he was the result of a broken condom and his "new" father was his real father.
Thanks for trying still not the one I was looking for the adopted boy was suppose to look out for the sister of the family thanks for trying sorry I don't ram remote
Not an orphan, so not the story you are looking for, one of the better brother protects sister stories is https://storiesonline.net/s/55910/an-unlikely-protector
IIRC Kenn Ghannon's Runesward has an adopted brother brought in to take over the family business. I can't recall more than that.