神秘之門突然出現於日本各地。在門另一頭的異世界「魔都」中存在著僅有女性在吃下後能獲得特殊能力的「桃」，人們為了消滅被稱為「醜鬼」的怪物，組織了由女性士兵組成的戰鬥集團「魔防隊」。尋求著能大顯身手的舞台的男高中生•和倉優希某一天誤闖魔都，並遭遇醜鬼的襲擊。此時連忙趕到的是魔防隊第七組的貌美組長•羽前京香。京香透過能力讓優希化身為奴隸，使其力量開花結果，並成功擊敗了醜鬼。從此他便以奴隸兼魔防隊管理員的身分展開了與醜鬼之間的戰鬥。

Japan, 2019, just before the dawn of a new era. Suddenly, a rift to another dimension appears in the sky, revealing an alternative world "Shinkoku Nippon," with the sky and the earth upside down. This parallel world keeps the former militarism, with its era being Eternal Showa. The military invades the real Japan with giant humanoid robots called "GARANN" and their gas weapons "GENMU", rendering our modern weapons ineffective. "Shinkoku Nippon" instantly seizes the government and achieves de facto conquest of Japan. The new era, "Reiwa," has not arrived for Japan.