Haruto, a young man from modern Japan, was once summoned to a fantasy world as a hero to defeat a demon king. After three grueling years of adventure and battle, he successfully slew the demon king and looked forward to his reward: a life of admiration from beautiful women and the harem he had dreamed of. Before he could enjoy any of that, political infighting among the kingdoms after the war led to his immediate and forcible deportation back to Earth. Cheated out of his one desire, Haruto refuses to accept his ordinary life. Using his own power, he forcibly returns to a fantasy world, determined this time to build the harem he wants without interference. However, the world he arrives in is not the one he saved. It is an unfamiliar land with its own established order, complete with a different hero and a different demon king. Stranded in this unknown setting, Haruto retains all the formidable combat strength and experience from his previous journey. He quickly demonstrates his overwhelming power, attracting attention from the local kingdom of Mirisha. He receives a request to train a new generation of heroes, and along the way, he begins to gather a party of women with the clear goal of adding them to his harem. His companions include the warrior Shalon, the mage Laurier, the maid Mina, Princess Ritina, the elf Ceris, and the beastkin Tanya, among others. The narrative follows Haruto as he travels through a series of locales, including the royal capital Mirisha, the city of Iris, the floating city of Angel, the port town of Belde, and the colosseum city of Odysses. His objectives are a mix of personal ambition, such as winning a trans-archipelago race in Angel to gain the fame needed for adventurer registration, and responding to larger threats, such as hordes of monsters flooding out of dungeons and the machinations of the demon lord's army. Later volumes see Haruto formally marrying multiple of his companions and even encountering members of the demon lord's Four Heavenly Kings, some of whom eventually join his party. The overarching conflict gradually shifts from simple harem-building to engaging with the demon lord's forces that threaten the world, all while Haruto continues to pursue his unapologetically crude personal quest.