JUMBO MAX: Hyper ED Yakumitsuzounin

Tateo Sone runs a pharmacy in Odawara and leads an ordinary but happy life with his beautiful wife and daughter-in-law. One day, however, when his wife tells him she is pregnant, he is shocked. It's because he has a secret: he has never had a functioning lower half of his body. His wife's child is not his own...Tateo despairs at the thought. At that time, a man named Sumaoka happens to give him a mysterious ED drug. Tateo impulsively takes the drug and is shocked to find that the function of his lower body miraculously recovers. Tateo declares to Sumaoka that he will recreate and make this medicine himself. But this is the beginning of a dangerous day that will change his life forever!

(Source: Big Comic, translated)