Designed by popular Japanese multimedia artist Toshio Iwai, "Otokki" or Otocky (which is the appropriate spelling that appears on the game's main title screen) was released for the Famicom Disk System in 1987. Otocky may be best described as a musical shooter. Your musical ship is able to shoot in eight directions. When you hit the A button, which is your main weapon, it plays different musical notes depending on which of the eight directions you fire it.
As you progress through the level, you can pick up power ups that are appropriately represented by little balls with an A or B on them. The A balls change the instrument that is assigned to the A button. Each instrument alters your attack rhythm slightly. The little round balls with B's on them allow you to get a secondary weapon for the B button but it has a meter and eventually runs out until you collect another B ball. You also collect musical notes until you fill up all five musical note symbols at the bottom of the screen. Presumably, each level continues to loop infinitely until you completely fill all five notes in the note meter or until your musical bubble weapon is completely depleted from your character being hit by the enemies.
Upon filling up all five note symbols, you are warped to the main boss of the level, which is a gigantic musical note with holes in it. This time as you fire your weapon the musical note meter decreases with each hit that you deal the boss. The only frustrating part of the game is the fact that if you are hit, not only does your main weapon shrink, but you also lose energy from the note meter located at the bottom of the screen. There are a limited number of notes that can be collected in each level. After the notes are collected, enemies appear in their place. This means that, unless you collect as many notes as you can without being hit, you can end up looping through the same level multiple times without ever reaching the main boss at the end.
Beating the game unlocks the background music player and a music editor that allows you to compose your own tunes. They both appear greyed out and cannot be selected on the opening screen before they are unlocked.
(Source: http://www.avantgaming.com/otocky.html)