While Retto and Kirira are off on their school trip to sunny Okinawa, the Saitama HXEROS branch comes under attack by a horde of Kiseichuu! Thanks to the help of a mysterious girl with a black HXEROS device, the whole Saitama squad winds up kidnapped. To make matters worse, this evil HXERO is the spitting image of one of Retto's classmates. Newly armed with the Naked Heavens Technique, Retto will do whatever it takes to rescue his comrades, and get answers about this mysterious anti-HXERO!