KiKi KaiKai (奇々怪界, lit. "Mysterious Ghost World") is a multi-directional shooter developed and published by Taito Corporation originally for Japanese arcades in 1986. Since then, the game has received a number of console and home computer ports in and outside of Japan, both as a stand-alone title and as part of compilations. The game originally saw a limited release in North American and European arcades as Knight Boy, a bootleg copy of the original Japanese version not officially licensed by Taito. In the English-speaking world, it is usually recognized as the forerunner to the Pocky & Rocky series.

Set in Feudal Japan, the player must assume the role of a Shinto shrine maiden named "Sayo-chan" who must use her o-fuda scrolls and ohari Gohei wand to defeat a number of renegade spirits and monsters from Japanese mythology. The game is noteworthy for using a traditional fantasy setting in a genre otherwise filled with science fiction motifs.

KiKi KaiKai is an overhead multi-directional shooter game that requires the player to move in four directions through various levels while attacking harmful enemies as they approach from off screen. As Sayo-chan, the player can attack by either throwing her special o-fuda scrolls in eight separate directions, or by swinging her purification rod directly in front of her. These techniques can be upgraded by finding special paper slips left by defeated enemies that will either enhance their power or improve their range. Sayo can be damaged by coming in contact with an enemy, and can only be hit once before she is knocked out and must resume the level from a preset continuation point. At the end of each level, the player must face a powerful boss monster that takes several attacks to defeat and is more difficult than normal enemies.

Several hidden items can be found by attacking objects with Sayo's purification rod, and can be used to either enhance her attack or grant the player points. Once a certain number of points are gained, the player will gain another life and have an additional chance to complete a level. When all of the player's lives are exhausted, a "number match" screen appears with a random 3-digit number in 50-base increments (100, 150, 200, 250, and so on). If the last three digits of the player's total score match the number displayed, they are granted a free game; if not, the game ends.

The Family Computer Disk System version of KiKi KaiKai introduced a few gameplay changes over the original arcade version, including new levels and enemies, as well as limiting the number of times the player may use Sayo-chan's ranged o-fuda attack, along with a second playable character: "Miki-chan", another shrine maiden who is designated as the player two character. Though several additional ports would be made over the years, each one would rely on the same basic game mechanics.