King & Balloon is a fixed vertical shooter wherein the player is tasked with defending a king avatar over protecting themselves. This gameplay conceit extents to the lives system; the character can die repeatedly, as long as the king is defended from the enemy characters above them. If the king is kidnapped three times, the game ends.
The game was built on the same underlying arcade hardware as Galaxian, and shares similar sound and enemy patterns. The exception to this is the inclusion of spoken voice samples for the king. When an enemy ship manages to evade your fire and seize the king from the platform beneath the player's avatar (two foot soldiers wielding a fanciful cannon), the king cries "Help!" as he is carried upward. The voice sample is different depending on the region; in the Japanese release, the voice sample uses phonetic English and sounds more like "Helupuru!" If the player successful rescues the king, the king expresses his gratitude by saying "Thank you!" with the same regional caveats.
Points are scored for destroying the balloon shaped enemies, who appear in Galaxian-esque ranks above the player. Scores are doubled for destroying balloons performing their dives toward the king. In addition, occasionally the different colored balloons will merge to form a striped balloon variant that requires three hits to destroy, and provides the player with significant bonus points for destruction.
Players are able to obtain one extra life once they obtain 10,000 points during play.
The game received an uncredited and poorly documented port to the Korean Sega Mark III. Based on the MSX port, the game (available on the Internet as a dumped ROM) runs in the Mark III's SG-1000 backwards compatibility mode. Beyond reorienting the game from a portrait aspect ratio to a landscape aspect ratio for home televisions, the gameplay remains much the same.
The game has been included in several Namco compilations over the years: