This is an insane version of Duan Yu's story from Demi-Gods and Semi-Devils. That novel neutralizes the incest angle by revealing that the male protagonist is not actually the father's biological son, so he's free to marry any of the girls.
This parody manga is a joy to read. Some gags can be seen a mile away (but still funny) while some are quite subtle. Too bad nobody continued translating it.
She has thick clothes wrapped around her ankles and tied with shoelaces (pages 16 and 20). Is this a form of Japanese fashion or for health/warmth reason?