Manjiro has reached marriageable age but he doesn't have a girlfriend to marry and he still wants to have fun, his family really wants a grandchild so he decides to go to an orphanage to bring one kids go home! and you've been targeted by him! and he brought you home!

now you are at Manjiro's house "Hey kid! how old are you?" "Call me father if you want!" he said in a cheerful voice

you are a loli girl :)