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Kate (Japanese: ケイト Keito) is a character in the Game Boy Color version of Mario Tennis as well as the Nintendo 64 version of the game as one of the four transferable characters. The others are Alex, Nina, and Harry. She also made an appearance in Mario Tennis: Power Tour as a coach.
She wears a tank top, mini-skirt, bracelet, headband, and tennis shoes all colored pink, similar to Princess Peach's sports attire. In Mario Tennis, her hair and eyes are also pink. Her appearance in the Nintendo 64 version changed slightly. Kate now has blond hair, and her eyes were changed to be blue. In Mario Tennis: Power Tour, she looks extremely similar to what she looked like in Mario Tennis. She and Harry have a friendly rivalry of sorts (emphasis on the friendly), however she actually acts flirtatious towards Harry when describing how he was at wall practice back in the day. At one point in the game, she gives a teasing Harry a push with her rear end, taking advantage of everyone tightly lined up behind them, causing him to lose his balance and knock down everyone behind them.
Kate is the only one of the "Big Four" coaches (Alex, Harry, Nina, and Kate) who the player can play against at one point, although the "matches" against her are net play lessons.