If I remember correctly, there was a family which I had been observing in the mundane world beyond Gensokyo, chewing on my hamburger.
There was a father and a daughter, in a really rich family, who loved each other very much.
It all started when he started coming to her room when she was a child. He would strip her then kiss her naked body. She liked his kisses and liked it best when he kissed her secret place. He would get naked and let her touch his hard cock and kiss it. She loved him to lick her and push his tongue inside her love hole. He would suck her flat titties and later they grew and he would suck them for a long time before he would kiss her secret place.
Soon she matured and daddy began to teach her to be a woman for him. Her tits had filled into nice large mounds and he taught her to shave her pussy for him. As he kissed her pussy he would then finger her love hole and as time passed he added more fingers to her. He taught her to not only kiss his cock but to suck it. He made her suck it down to his balls. At first she would gag but she got to be a great cock sucker for her dad. He fucked her mouth hard as she sucked and he would release his cum in her and she would swallow all of it.
The first time he fucked her tight cunt was very painful. He had a big thick cock and had a tough time burying it in her tight hole. The first night he fucked her three times filling her with his cum. Afterwards he would lay and suck her tits as he played with her pussy till he was hard and ready to fuck again. Soon he was fucking her all night and cumming in her many times. He either fucked her mouth or her cunt. He was never satisfied and he could fuck for hours.
He then told her to stay naked all day and they would fuck every where in the house. He fucked her while she was cooking and then when he sat to eat, he had her suck his hard cock. Just seeing her pussy would make him need to fuck her. he would lay her on the table and fuck her for hours filling her hole with cum. When ever he walked by her, he would finger her cunt till she would cum over his hand and then he would let her lick her cum off his fingers. Sometimes he would rub the cum over her nipples then suck the nipples.
One day when she was naked, he leaned her over the chair and spread her legs. He felt her pussy and then her ass. He spread her ass cheeks and pushed a finger up her ass. His cock got so hard he then pushed his huge rod into her ass. It felt good to be in her tight ass and he fucked her without mercy even as she cried in pain. He came two times in her ass and then he finger fucked her cunt. Now he could have sexual relief in her ass when she was bleeding with her period. Several times that day he fucked her ass with his huge cock as his fingers filled her cunt.
Several weeks later after they had fucked all night she told her dad she may be having his baby. And she was right. As the months went by, her tummy swelled and her tits grew and filled with milk. Her dad would now suck the milk from her huge tits loving the tasty liquid. As she got too big for fucking her cunt, he kept fucking her ass and she would suck his cock. He would lick her pussy and suck her cum from her hole. He still kept her naked and loved to see her huge belly. He would sometimes jack off on her belly and rub the cum over it.
The baby was born at home. It was a beautiful girl. She would nurse both the baby and her dad daily. As daddy nursed her full tit he would finger fuck her cunt. sometimes he would finger fuck her ass as he sucked her tit. He still fucked her ass several times a day but soon he would be able to fuck her cunt again.
Over the next several years she gave birth to two more daughters and a son. As the children grew older, it was time for daddy to teach them about sex as he had their mother. He soon was fingering and fucking all three daughters. He would bring them in one at a time to his bed and their mom would hold them as he fucked them. They all would nurse her tits full of milk. they soon had the son nursing his moms tits too. Soon the son was fucking his mom as the dad fucked a sister. Then the son would fuck a sister or a sister or two would suck his cock.
The dad then taught his son to fuck his mom and sister in the ass. The dad loved to watch them get their ass fucked by his son who had grown a nice huge cock. Then one day he asked the son to fuck his ass as he fucked the mother. Then he let the son fuck the mother as he fucked the sons ass. He was surprised how much he loved the son fucking his ass. And he loved watching his daughter and son fuck each other.
Over the years, more babies were born and no one knew for sure who the daddy was. It could have been their dad or their brother who bred them. But as each got older, they also were fucked too.
Now, if remember correctly, that family goes by the surname Scarlet... and it had its descendants scattered all around the globe, that is, until the exorcists considered them as demonic and killed off all of them and as such, the surviving ones fled to Gensokyo, and stayed there ever since ever since.