Kaette Kita Moto Yuusha

A hero was once summoned to another world to defeat a demon king. After a three-year conflict, he successfully killed the demon king and was sent back to Earth. Upset about being separated from the various races he had grown fond of, he expresses frustration over not being able to build a harem in that world. With no magic on Earth to satisfy his desires, he decides to return to the other world on his own. This time, he plans to avoid being sent back and focus on creating the harem he wanted.