In the future, humankind came under a fierce attack from aliens. The population has not develop technologies to adequately reflect the enemy attack and a lot of people just waiting for their death. After a while, when most of humanity was destroyed, in the secret cave found a heavy duty weapon that became the salvation of the entire planet. After the war, people had hero - Ryusei. This guy was able to harness the unknown device to fight the monsters. One year later, while the areas which had been destroyed by the aliens were still being rebuilt, Ryuusei was appointed as the commander of the newly-formed Defence Force of Earth, which was created to fight against space invaders. However, he was the only person who could use the ‘imagination embodiment device'. If something was to happen to him, then calamity would befall the world. So the Defence Force of Earth decided to recruit girls with potential to fight alongside him and they were called Blade Riders. Ryusei also got sexually involved with girls.