Prince Kinnikuman, who came to Earth from Kinnikusei, a planet at the end of the universe, was always ridiculed by humans as a useless Chojin. However, by chance, he was given the right to participate in the Chojin World Cup, a tournament to determine the world's best Chojin, and by a miracle, he won the championship. The following year, he even won it again! Since then, he has become a central figure among Seigi Chojin who protects the peace of the universe. He has managed to defeat the raging forces of the enemy, including Akuma Chojin who plans to rule the world, and Perfect Chojin who aims to wipe out the weak Chojin on Earth, with the power of friendship with his friends, including Terryman and Robin Mask. In recognition of his achievements, Kinnikuman wins the "Survival Match for the Kinnikusei Throne," the final test of his career, and is crowned the 58th Great King of Kinnikusei! He returned to his home planet from Earth, got married, and said goodbye to eight years of fighting. About a year and a half later, the entire universe was supposed to be at peace...

The year is 20XX. The ninja, who once forged the history of Japan, were scattered across the country during the Meiji Restoration. As these ninja mingled with the other clans, their bloodline thinned, and they gradually faded from sight. The descendants of these ninja clans, seeking to preserve their heritage, formed the WNA (World Ninja Association) in the hope of carrying on their legacy. And so it was that the WNA succeeded in developing Ninja-Gum, an art which could summon forth the strength of the Shinobi. And yet creating the most powerful Ninja-Gum requires the strongest of ninja DNA. So it was that the Ninjala Tournament was held, that the mightiest of all ninjas could be found...

High school student Taiyou Asano has been socially inept ever since his family died in a car crash. The only person he can properly interact with is his childhood friend, Mutsumi Yozakura—the head of the world's strongest family of spies. Mutsumi's eldest brother, Kyouichirou Yozakura, has been overprotective of her ever since he once rendered her severely injured. His love for Mutsumi is lethal, and Taiyou is his next target. To survive, Taiyou must marry Mutsumi and become a member of the Yozakura family. Thrown headfirst into chaos, Taiyou begins his journey to become a powerful spy in order to protect his wife and uncover the dark secrets of his past and the Yozakura family.