Iyashinbo ~Sekai de Ichiban Suki na Hito~

Makoto is a high school student. He lives together with his mother, Tamami, because his father passed away when he was a kid. One day, his dick gets erect as usual when he wakes up, but never gets small. Tamami finds it, and immediately takes him to a hospital. According to the doctor, he has a continuous erection disease, and is required to ejaculate periodically. Since then, she gives him a blowjob every time necessary. However, she gradually gets sexually excited....

[Edited from ErogeShop]