3点到7点(⁄ ⁄•⁄ω⁄•⁄ ⁄)我只想说大兄弟你肾亏不？

Base +6, CX~DeribuRa -30, Guardsman40k -5, freespace2 -7

In the first part it's shown he isn't her real father, but a neighbor with whom she begins a sexual relationship. He reminds she and her mother of her father, so it's implied she hooks him up with the mother, and as shown continues to fuck him in return.

Base +6, FO-Bakayarou +10

Hoping to see the first part

Base +6, FO-Bakayarou +10

The prequel was released in Comic Kairakuten's 2015-09 issue. The girl's (Asuka) dad passed away some time ago, so it was just the mother and her. The mother suggested Asuka be nice and go check on the neighbor.
The neighbor in question was a lonely older man who recently lost his job, who'd be around her deceased dad's age (The mom commented that the dude reminded her of his husband). Asuka initially starts by taking some leftover dinner to him, then cooking for him herself, but one thing leads to another and she starts doing sexual favors for him, eventually treating him as her "sugar daddy".

So this is in no way incest at all, not even inseki.

Base +7, FO-Bakayarou +10