There is Gamma Universe where Women are all Immortals.
But men are all mortals. They attain maturity at 20 years old. They become stronger day by day and they die suddenly, When they reach 40 Years old.
They both never age after they attain 20 years old.
The universe is started by woman named Lilith, She come to the universe pregnant and give birth to a baby. She suffered a lot and control her desire. When the baby grow and become adult of 20 years old and attain maturity, She become so happy and it's the time for her to be happy and enjoy the fruit of her own tree.
The 20th birthday of every first born male have a ritual and it happens only in a Ritual sites. The rituals Starts with him having s3x with his mother in every position which is drawn in ritual site. The ritual finish only when he finish doing his mother in all s3x position mentioned in ritual site.
The First born son become the s3x mate of immortal mother and he will be the partner in sex until he attains 40 years old and die. She normally give a birth every year of his 20 years of life. After he dies, She choose the first son she give birth by her dead husband (Son). When the current First son become 20 years, the rituals began and it goes on like continuous cycle.
Female child a mother gives birth too can have ritual (First time s3x) with any of her matured(20+) aged brothers except first born, Because he is reserved for their mom. They can have s3x with any one of their brothers until they give birth to their own child.
When they give birth to their own child and when the child reaches maturity, the rituals are all carried by their son.
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