In the future, overpopulation is a serious problem. It all stems from the "Mega-Playboy" who passed his playboy DNA on to his one hundred children, who in turn had one hundred children each, and so on! Karin Aoi, a DNA Operator, has traveled back in time in order to change the DNA of the original "Mega-Playboy"--but is Junta Momonari really him? He can't even look at a girl without throwing up!

Karin's job well done has turned into a disaster! The DNA Control Medicine was supposed to rid Junta of his lady-killer genes, but instead she's accidentally forced him to become the legendary "Mega-Playboy"! Worse yet, he's already begun his conquest, starting with Tomoko, the most popular girl in Junta's school. But Tomoko's already got Ryuji, and her boyfriend's not afraid to let Junta know it

Junta's "Mega-Playboy" DNA hasn't stabilized yet. One minute he's suave, and the next he's struggling not to puke on a girl's shoes. Before the DNA can take hold fully, Karin launches a plan involving Junta's childhood friend, Ami. Could it be that the Mega-Playboy's charm doesn't work on everyone?

Hearts are aflutter and emotions run high as Junta's "Mega-Playboy" DNA starts coming into its own. But while Ami, Tomoko, and even Karin struggle with their feelings, Junta's made up his own mind. To express his true feelings, Junta plans to buy a present to give to the girl he loves. But who's the lucky girl?

Ami's friend Kotomi has a crush on a boy. Unfortunately for everyone involved, that boy is Junta. With yet another heart added to the mix of bubbling romances, Karin becomes desperate to get Junta together with Ami, the only girl immune to the Mega-Playboy's charms, and the only one that might tame the lady-killer-to-be.

After humiliating herself, Kotomi runs off and completely changes her image. Her new look is red hot, but Junta still isn't interested--until he realizes that the two of them are more alike than he thought! Can Kotomi press her advantage enough to win the heart of the budding Mega-Playboy?

Junta thought he'd never get a girlfriend with his problem. Kotomi thought she'd never get a boyfriend with hers. Sharing similar embarrassing problems, Kotomi and Junta practice together in order to overcome their difficulties, but will that be enough for Kotomi? Meanwhile, Karin tries to convince Ami, and maybe herself, of what's best for the future.

Kotomi forces the issue of her feelings for Junta, and Junta's Mega-Playboy persona takes over and tells her what his feelings are for her. Meanwhile, Ami tries to figure out her own emotions concerning Junta, while Karin wonders why the Mega-Playboy held himself back from taking an all-too-willing girl.

The solution has arrived from the future: the real bullet Karin was supposed to hit Junta with! The DNA Operator lures Junta to the roof of the school building, where she lines up her shot. But fate intervenes, as Tomoko and Ryuji, arguing over their relationship, are also on the roof. Karin takes her shot--but does it work?

Having been shot with the DNA Control Medicine, Ryuji discovers that he's been given the ability to shapeshift! His first order of business with his new powers is destroying Junta's life--starting with alienating him from his friends and the ones who love him. After he taunts Junta's powerlessness to stop him, Junta makes up his mind on how he'll beat Ryuji.

With no way to complete her mission, Karin is ordered to return to the future. But it's an order she has to refuse, because it's not over yet. If she returns now, Junta will be forced to fight Ryuji, and that could very well mean the boy she loves may die! Rushing to Ryuji's manor, Karin finds that Ryuji is anything but himself, and that her worries are all too real.

Ryuji has become like a god, his physical prowess beyond anything human. All he cares about now is to destroy his rival, Junta Momonari! Fortunately for Junta, he's also the only one who can stop Ryuji now... or rather, the Mega-Playboy can! But if he becomes the Mega-Playboy one more time, he may change forever, dooming the future... and if he doesn't, he's dead!