otocky was designed for the famicom disk system by toshio iwai, the interactive media installation artist who would later create electroplankton for the nintendo ds. otocky is not a rhythm game; rather - like rez much later - it's a shooter where the player's actions create music.
the player soars through a horizontally-scolling landscape of cubes and globes, factories and giant keyboards. each stage has its own beat. the player is armed with a ball that can be fired - using the A button - in eight directions. each direction corresponds to a musical note. when the player shoots enemies (contact with whom makes the ball smaller and smaller until the player tumbles from the sky) the player adds notes to the beat playing in the background, making music.
using the A-button ball, the player needs to collect musical notes which hover and hide and dance in the architecture of the stage. the stage loops until the meter at the bottom of the screen is filled, with enemies replacing the notes the player's already managed to nab. when the meter shows a full five notes, the player confronts a huge musical note riddled with holes, out of which stream hordes of malicious creatures. the collected notes must be used to patch those holes and end the stage.
in addition to notes, the player can collect - simply by touching - A bubbles, which change the player's instument and weapon, and B bubbles, which provide the player a B-button "bomb" weapon. this limited-use weapon comes in a variety of shapes which can be used to escape tricky situations. there are also other items which provide other effects, like "fast fowarding" or slowing down the speed of the game.
the game also has unlockable play modes, including a "bgm mode" where a cleared stage is played with no score and with no enemies, for the simple purpose of improvising music, and a "music maker" mode where the stage's music can be edited by the player.
otocky is a fabulous and increasingly difficult excersize in improvisational music. if you don't have a famicom disk system, you might like a rom of the game. to run it you'll need an emulator that supports the disk system and some music in your heart.