In the future, society has a major population problem. The cause is the Mega-Playboy — men who are totally irresistible to women, due to their genes. One Mega-Playboy can make over 100 women pregnant and the male offspring in turn also becomes Mega-Playboys.

Karin is an agent sent to the past to find the first Mega-Playboy and stop him with a special genetically tailored bullet. Karin, who dreams of having her very own "Sweet Home" (a rarity in the overcrowded future), finds the original Mega-Playboy — a young man named Junta. Junta has a problem; he throws up at anything even remotely sexual. Perplexed, Karin tries to complete her assigned job anyway, which goes badly wrong.

Other players in this twisted plot are Ami, a girl that Junta grew up with (and the only female he does not get sick around), Tomoko, first victim of Junta's Mega-Playboy powers, and Ryuuji, the jealous boyfriend. Not to mention the hordes of girls who swoon when Junta powers up, including Karin.