Kathy (キャシー) is a worker and performer in Hamegg's Robot Circus. She is one of Astro's first friends and an ally of Dr. Ochanomizu. Her Japanese voice actor is Rihoko Yoshida, and her English voice actor is Patty Whitely.
Kathy is a confident and outspoken young woman, working on maintenance and management with the Robot Circus. She is unafraid of talking on a casual level with her boss Hamegg, or even with the Chicago mafia don. Kathy initially doesn't want to work with Astro (whom she meets under the name of Tobio/Toby), assuming he'll be too much trouble alongside her other circus duties. However, she soon becomes very sympathetic towards him, treating Astro like a younger brother.
Kathy believes very much in Astro, to the point of betting Hamegg that she can train Astro to safely perform the 50,000 Volt Trapeze. She frequently steps in between Hamegg and Astro to prevent the boy from being beaten. Kathy later helps fake Astro's fatal explosion, and smuggles him away from the Robot Circus to help Astro escape with Dr. Ochanomizu. It is implied that she is still safely working with Hamegg and the Robot Circus.
She has bright red short hair and brown eyes. She wears an outfit based on the American flag, with a white and pink striped shirt and star-dotted blue jeans.
In the 1980 series, Kathy is the one who gives Astro his iconic red boots. She explains that they originally belonged to her, and wants Astro to have them as a good luck charm. Later, she suggests that Dr. Ochanomizu rename Astro from Tobio on account of his atomic-based power system (leading to "Atom" in the Japanese version.)