Block Crash 123 is a Hello Kitty-themed Breakout clone featuring illustrations from popular Japanese artists such as okama and KEI. There are ten characters to choose from, one from each of the ten featured artists, and twelve stages for each. The game plays like most any other Breakout clone: hit the ball with the paddle, trying to destroy all the blocks with it without letting it fall out the bottom of the screen. Run out of lives, and the stage must be restarted. Blocks occasionally drop power-ups (or power-downs) when destroyed, which will give a temporary effect to either the ball or the paddle when picked up.

The player can choose any character, but the stages within must be done in order. Completing all stages for a character unlocks their illustration, and completing all characters unlocks a bonus stage. Each character's stages feature different themes and gameplay gimmicks; for example, one character's stages include blocks that slowly advance downward, while another character's stages are played with the system on its side.

There is also a clock & calendar mode, where the player can select from unlocked illustrations and a variety of visual designs to create a custom-design clock. The complete list of featured artists is: okama, KEI, Teruhiko Imaizumi, Poyoyon Rock, Keito Koume, Shimeko, Kohaku Kuroboshi, Aoi Nishimata, Eiji Komatsu, and POP.

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