Jamiko Miyamoto is the main protagonist of "Seigi no Senshi Captain-Japan", a shy, kind-hearted and friendly 10 year old kid who is from a long line of samurai heroes. He never fights out of anger or revenge, he only fights to protect his friends and the people of his home town (Neo Tokyo) from Destruction's mutants. His Japan-unit (a transformation device) is on his wrist and his activation call is "HENSHIN!!". When Jamiko was 3, his parents, Ryu & Sakura Miyamoto, were killed when Lord-Destruction sent some of his mutant-warriors to attack the dojo where he lived. Jamiko was placed in the care of Man-Chu & Doggie Krugger (the head of S.P.D).

Captain Japan. Jamiko's superhero alter-ego. Unlike Jamiko's normal self (sweet and shy), CJ is a wise-cracking ass-kicker, but he still has a kind heart and a strong sence of justice. He main weapon is a modified samurai katana sword called The Samurizer-Sword, he also has access to all sort of battle tested weapons such as the The Samurizer Pistol, the Hyper-Shovel and the Buster-Scissors . His finishing attack is called the "Katana Rappa", a powerful slash which slices the opponent in half.