Kaettekita Motoyuusha

Once summoned to a fantastical realm to vanquish the Demon King, a valiant hero spent three grueling years fighting a relentless war. After finally slaying his ultimate foe and saving the world, his reward was anything but heroic. Instead of being celebrated, he was unceremoniously dismissed and forcibly deported back to Earth, stripped of his hard-earned place in the world he had just rescued. Frustrated and bitter, the former hero laments his fate. Earth is a mundane planet entirely devoid of magic, making his greatest personal ambition impossible to achieve. He had dreamed of building a grand harem alongside the beautiful elves, beastfolk, dwarves, and demons he encountered during his journey, only to have that fantasy snatched away at the moment of his triumph. Refusing to accept such an unjust ending, he resolves to take matters into his own hands. Using his knowledge and abilities, the hero orchestrates his own return to the other world. This time, he will not repeat the blunder of allowing himself to be exiled back to a magicless reality. With the Demon King already defeated and no obligations holding him back, he sets out on a new quest: to finally build the harem of his dreams in the magical realm he once saved.