Eh they are unrelated, they're both adults, and she has daddy issues. Seems fine to me. Nobody's taking advantage of anyone else and they are just trying to be happy.
Also gotta love Akira still doing his naked all the time thing even though he lives with Misaki now. Was thinking it would've actually been funnier if Minami established from the start that Misaki was going naked 24/7 in their apartment too. Not because of the fan service (well maybe a little) but because the absurdity of it would have been hilarious.