>>283624988
I remember playing a mobile game with almost similar plot ages. You find an elf girl in the forest and raise her as your sister. Depending on your choice, you can raise her as a warrior, a mage or a housewife and many other choices. Sadly can't find that game in play store anymore.
I found it because I used to just type imouto in the search bar and find and install random Japanese looking games. I don't think playstore allows any such games anymore.