Kyonyuu na Tomodachi no Haha o Wakai Kyochin de Netotte Haramase Harem o Tsukuru Hanashi

A world in which men who can achieve erections and ejaculate are becoming rarer and the problem of declining birthrates is becoming more serious.
Meanwhile, the protagonist has an incredible sexual prowess and a huge penis, but he can't bring himself to tell anyone around him, and he spends his days being aroused by his friends' beautiful, busty mothers.
One day, the protagonist is informed of its rarity by Mizuho Mama, who witnesses an erection, and as a result of the formal procedures, is issued an "insemination permit" by the local government.

A man's right to have an erection - to be able to impregnate any woman he likes!

The protagonist immediately impregnates Mizuho Mama, succeeding in making his friend's mother's pussy go crazy for him and corrupting her.
And so began a dream-like life of impregnating and using as sex toys all the time the busty, beautiful mothers of his friends who had been making him horny for so long.

[Translated from DLsite]