Kaette Kita Moto Yuusha

A hero was once summoned to another world to defeat a demon king. After a three-year war, he succeeded and was sent back to Earth. Upset at being separated from the elves, beast race, dwarves, and demon race he had grown close to, he expresses frustration at missing his chance to build a harem in that world. Determined to fulfill his dream, he returns to the fantasy world on his own. This time, he plans to avoid being sent back to Earth and create the harem he desires.