Isekai Tennis Musou centers on a high school tennis sensation who gets transported to a different realm as a hero, only to find it lacking compared to the intense competition of high school tennis nationals. In this world, tennis serves as the ultimate superpower, allowing him to obliterate dragons with a single strike or vanquish hordes of demons. However, he faces a formidable opponent in the demon king, who proves to be a skilled tennis player as well.