Ninja-kun was originally released in 1984 by UPL as an Arcade action game in which the titular diminutive shinobi has to climb and descend a group of platforms to take out every enemy on the stage with their shuriken, which could only be fired left or right. Clearing the stage of enemies would move the player onto the next, and the stages would eventually start recurring similar to other Arcade games like Donkey Kong.
Jaleco ported the game to the Famicom in 1985. UPL would handle the Famicom conversion for their 1987 sequel, Ninja-kun: Ashura no Shou. Since then, the Ninja-kun games have seen a few more adaptations and remakes, and Jaleco would go on to produce the similar Ninja Jajamaru-kun games for various consoles. In US and Europe territories, the Ninja-kun games are known as Ninja-Kid.
Ninja-kun was also referenced by the GameCenter CX/Retro Game Challenge games: their Haggleman character was based on Ninja-kun and Ninja Jajamaru-kun.
The 1983 Ninja-kun game from Microcabin isn't considered part of this series, but is one of the major influences for UPL's 1984 Arcade game. The 1986 NES game Ninja Kid from TOSE/Bandai is not a Ninja-kun game either; rather, it is a graphically-modified Gegege no Kitarou licensed platformer with some similarities.