Ore to Okaa-san no Haramase Skinship

The protagonist's family is a branch of an old family. Due to an old tradition, the mother is forced to have another child. The protagonist, who has always had feelings for his mother that are greater than those of his immediate family, dreams that he will be the one to sire the child, and his love for his mother grows stronger.

Then, his father goes away on a business trip for a few weeks for work. That night, the mother sneaks into the protagonist's room. Unbeknownst to the father himself, a serious illness a few years ago has reduced his sperm count to the point where he is unable to conceive naturally, so he wants his son, the protagonist, to fulfill that duty.

She doesn't want to do it, but it's still the customary thing to do,and the hero embraces his mother, who is in tears. He says, "If it's okay with you, I'll get my mother pregnant. The mother smiles happily at his words. As he hugs her body again, the protagonist feels a strong desire that he has never felt before.

He wants to make her his while his father is away, and he tells his mother that he read on the Internet that the better you feel, the more climaxes you feel in a row, the easier it is to get pregnant. My mother's eyes light up at his words, but her cheeks blush as she wonders if that is not a bit too much. The protagonist smiles kindly and says that if it were a stranger, that might be true, but if it were his own son, he would have no problem making her feel comfortable and at ease.

The mother blushes again at that smile and gives him a happy and lustful look, wondering when he learned to look so nice. Then, to get started, the hero picks up his mother's body and lays it on the futon. When he sees his mother's eyes go down, his desire explodes...

[From official site]