Modaete yo, Adam-kun

In a world where a pandemic has afflicted mankind with erectile dysfunction, high school student Kazuki is the only one who can still get an erection. If his secret is discovered, he could be condemned to a life as a guinea pig... He doesn't want that! He transfers to a new school in order to protect his secret, only to find out that it's a harem school full of women!? Sure enough, he can take any woman his prisoner: a friendly and amiable senior, a sexually frustrated teacher, the school's "prince," the scion daughter of a conglomerate... This is the story of one Adam being pursued by four billion Eves.

(Source: Suiseisha, translated)