Kimomen Demo Kyokon nara School Caste no Chouten ni Tateru!? ~Gakuen Ichi no Motekawa Shuudan ni Tanetsuke Shimakuri! Yume no Gakuen Harem!~

In the near future, where men's penises and purposes had shrunk to miniscule size, the birthrate had dropped to dangerous lows. Everything came down to one valuable asset: having a massive cock! Big, fat, thick, fully engorged wangs are worshipped by a female society deeply in need of satisfaction! Enter our hero, an unattractive guy with the lowest status of anyone at school... until it's discovered that he's got a cock like Popeye's forearm! From loser to lover, celibate to celebrated, experience the dream harem-fucking rise of one lucky man born in the right time, at the right girth! [Edited from DLsite English]