Karin, a DNA operator from the future, is on a mission to change the course of History by stopping Junta Momonari from becoming the Mega-Playboy who fathered 100 children and led to the overpopulation of the world. But Junta is no playboy; in fact he is allergic to girls. But when Karin shoots him with the wrong DNA-altering bullet, he starts sporadically becoming the Mega-Playboy capable of charming any woman. Karin must try to restore the situation to normal before the change to Mega-Playboy becomes irreversible.

[Source: Anime News Network]

Junta's great granddaughter goes back in time in order to make Junta stay as the Mega-Playboy so she can continue to exist. Along with her comes an old man with the intention of making Junta stay as the Mega-Playboy forever for his own purposes.When Junta starts getting attacked, he has no choice but to return to being the Mega-Playboy in order to protect his loved ones.