Ninjakun (忍者くん魔城の冒険 Ninja-kun Majō no Bōken?, lit. Little Ninja Adventure at Demon Castle) is a ninja action arcade game that was only released in Japan. It employs a cute artwork style and features the player as a red clad ninja facing an army of enemy ninjas and demons. The player must defeat each and every enemy in a stage in order to advance to the next stage. Each stage takes place in a vertically scrolling mountain or castle, and the player and enemies jump and fall between different levels. Ninjakun was ported to the Famicom and MSX systems. The Famicom conversion was done by Jaleco, who produced a Famicom only sequel Ninja Jajamaru Kun which was released for the Wii Virtual Console in Japan. UPL produced an arcade sequel known as Ninja-Kid II, which they ported to the Famicom as "Ninja-kun Ashura no Shou".

• Ninjakun starts out at the bottom of every stage. Eight enemies will be distributed throughout the stage.
• Ninjakun must defeat all eight enemies with his throwing stars within the time limit in the stage in order to advance.
• In stages 3 through 24, one enemy will be one degree of strength higher than the other seven.
• Ninjakun may touch or bounce off of any enemy, but he will lose a life if he is struck by an enemy projectile.
• If the player bounces on the enemy's head, the enemy will be stunned. The reverse is also true.
• Pick up scrolls for bonus points at the end of the round. Catch glowing orbs and enter a bonus round when you collect three orbs.