After the game's ending plays, there are several things that will happen if the game is left running, and it's possible to trigger a hidden message from a programmer named Hidemushi. First, the ending photo will change to black and white after waiting 18 minutes, and then sepia after another 18 minutes. After 55 more minutes, the music will then stop, and pressing A + B + Start + Select + Left on Controller 1 and A + B + Right on Controller 2 will cause some new music to play. Pressing B + Select + Right on Controller 1 and B + Right + Down on Controller 2 will start Hidemushi's message, calling out everyone that he had to put up with while developing the game and thanking those who did help him. Once Hidemushi's message stops, press A + B + Up on Controller 1 for his last message, a dedication to his wife. After waiting 18 more minutes, the game goes back to the title screen.

Two exclusive songs play during this hidden message. The first track is a remix from The Karate Kid NES game, while the other track is completely new and starts playing when the message 「そういえば　せわになった ひともいたな・・・・・」 appears, translated in English to "Come to think of it, some people were helpful to me, too." Both games were composed by Hirohiko Takayama. Both songs, unlike the rest of the game, use the Famicom's basic onboard audio system rather than the Namco 163 audio expansion chip which supports up to 8 additional channels.