Study Japanese culture, manga, anime and history. A Japanese superhero needs to conform to the society of Japan and should not alter the history of the country. Manga, which are Japanese comics and anime--Japanese motion-picture animation--can give a good idea of how to depict a Japanese superhero.
Design a basic personality for the character. All superheroes need to have a distinct personality. A superhero in Japan would hold the good of others and family honor above personal safety and comfort. Beyond the basics needed for a hero, the personality traits are your choice.
Design a costume. A Japanese superhero, like an American superhero, will usually have two basic designs: the hidden identity and the superhero identity costumes. A famous example would be Sailor Moon and the other Sailor Scouts, who typically have a design of normal girls in the normal school uniform and the superhero design that comes with using their super powers.
Give the character human traits. A good superhero, Japanese or otherwise, needs to be mostly human. For example, Sailor Moon is clumsy and poor at school. In Japanese story lines, the superhero characters are usually those that have strong, protective feelings toward friends and family, but are usually not very good at everyday living. This is a strong theme throughout Japanese manga and anime.
Give the superhero a code name or superhero name. Japanese heroes have superhero names just like American superheroes, such as Sailor Moon and the Sailor Scouts.
Give the superhero an enemy. Enemies are an important counterpart to any superhero. There cannot be a superhero without a super villain. Decide on a villain and the superhero's motivation to get rid of the enemy.
Determine what the superhero's abilities are. Common abilities in Japanese manga are related to martial arts, such as a strong punch or fighting abilities. Japanese superheroes will often use technology or machines rather than having a specific talent. There are some heroes, such as Sailor Moon, who have abilities like the use of fire, water or other elements.