Akakage aka The Red Shadow was one of Japan's very first superheroes who existed back in the mid 1500s.
Akakage was a man in his mid 20s with dark black hair who wore dark blue ninja garb with gauntlets that housed his shurikens and a katana hostered at his waist. He also wore a red scarf around his neck and red domino mask that covered his face to hide his identity.
During a battle against Shocker to stop an operation where they were hijacking a new quantum energy device, the Kamen Riders accidentally opened a tear in spacetime and wound up being transported into feudal Japan via time warp. There, they witnessed the adventures of a masked ninja, a bird samurai, and a heroic demon who used sound as a weapon.
A young nameless ninja in the employ of a daimyo was sent to assassinate a rival lord for burning the crops of his land and killing his villagers and warring with him over territory. The ninja was going to kill the rival daimyo, but saw his frightened children watching and hesitated for a second. The damiyo then stabbed him with his own sword and revealed he was a demon and the children were an illusion created by him. The ninja fled before he could be killed and went into hiding out of shame for failing his mission. At first he considered suicide by hanging himself from a tree, until he saw a young boy drowning in a river nearby and saved him. The boy's grandfather, a shrine priest, thanked him for saving his grandson and gave him their shrine's sacred power, a blood red mask endowed with mystical energy of the Shinto gods that could dispel and kill demons. After donning the mask, training and defeating the demon daimyo, the ninja found his purpose: to exterminate evil demons wherever they may roam and christened himself as Akakage. The priest and his grandson aided him as Aokage and Shirokage using their skills to help him defeat evil. Some time afterward, he joined forces with a samurai named Hayate and an Oni named Hibiki to battle the demon Orochi who was being controlled by the Blood Wheel Ninja Clan-Makamou alliance.
The two Riders, who were traveling with them, were returned to the present before they could witness the outcome of the battle. However after visiting a museum exhibit, they found Akakage's mask and scrolls that detailed his heroic deeds as well as a message for Hongo and Hayato stating that he lived a long life and got married and that the Red Shadow will live on into their time. The episode ends with a scene in Shibuya with a bank robber possessed by a demon battling a red and black blur, The blur is revealed to be a silhouette of a young girl with only the red mask on her face shown having her injuries tended to by a boy in a priest's garb, whom she calls big brother and Shirokage. This implies that the mask in the display case is a fake and the real one is in the possession of Akakage's descendants.
Akakage was a skilled swordsman and user of shurikens. He was highly trained in various styles of ninja combat and due to the time warp caused by the Double Riders, he had access to grenades, a weapon that would not exist for hundreds of years. His signature weapon is his mask, a holy relic of incredible power that fired a beam that exorcised and destroyed demons and enhance his sword attacks.