Cat's Part 1 casts the player in the role of an unnamed protagonist, presumably young, male, and very interested in the members of the opposite sex. One fine day he meets Stella, the queen of magic world. She tells him that her duty is to sustain the balance between worlds, but now her power is fading, which means a new queen has to arrive and take her place. To find this queen, Stella tells her companion Pixie to open the gates to seven different worlds: three modern-day ones, three futuristic ones, and one "past", and sends the hero on the quest for balance in the world... and numerous sexually fulfilling encounters with pretty girls from different dimensions.

The game plays like a traditional Japanese adventure, which still pictures, plenty of text, and the necessity to go through all the commands several times to trigger new ones and eventually advance the story. However, unlike most games of this kind, Cat's Part 1 features a point-and-click interface along with the usual menu-based choices. Thus, the player can interact with various body parts of the girls, as well as some objects, by simply clicking on them.

The player must complete Modern World 1 first, but after that is free to travel to the six remaining worlds in any order. It is also possible to teleport out of the world at any time using a magic stone.

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