I was astounded to know the author is a woman. It completely changed my perception of this manga.
If the author were a guy, then fantasizing grooming a little girl to be his bride is just standard manga degeneracy.
But for this to be a woman's fantasy instead, I'm actually surprised how mature and so against it the male lead is.
Still, it's nice to know women can be degenerates, too. 😉
I think she was never legally adopted. When Daikichi asked Rin about becoming her official dad, she refused it outright, and insisted that she just sees Daikichi as Daikichi, which probably implies Daikichi only became a legal guardian.