Kate 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 lipstick, a tank top, mini-skirt, bracelet, headband, and tennis shoes all colored pink, similar to Princess Peach's sports attire, along with blue eyeshadow. In Mario Tennis for the Game Boy Color, her hair and eyes are also pink, though her appearance in the Nintendo 64 version is changed slightly, giving her brown hair, blue eyes, a white tank top, and a blue skirt. In Mario Tennis: Power Tour, Kate now has blond hair and her eyes were changed to be blue, though the rest of her attire is similar to her appearance in the Game Boy Color version of Mario Tennis.
She and Harry have a friendly rivalry of sorts, however she actually acts flirtatious towards Harry when describing how he was at wall practice back in the day. At one point in the Mario Tennis: Power Tour, she gives Harry a teasing 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 in Mario Tennis: Power Tour, although the "matches" against her are net play lessons.