While you tell Hello Kitty to run left and right, blocks fall from the top of the screen of different colors. But if she falls through the floor into nothingness, the level has to be restarted. It's not deadly, but she'll be out of commission for a few seconds after a particularly nasty fall. She'll also act like a Lemming by falling off edges - so be careful, since she'll stun herself if she falls too far. She'll climb up single blocks in her way, but walk the other way when there are more than that. While you're not in complete control of Hello Kitty, you can tell her to walk or run to the left or right by holding down the Select button and pressing left or right. Guide Hello Kitty around the playfield to collect icons - collect all the icons, and you've cleared the level.
The idea is very much what you'd get if you crossed Lost Vikings with Tetris.
