He and Kaoru have a good friendship, despite them having a liking in the same sport. He was inspired by Kaoru and wanted to learn more from her. When they were young, they shared the same story.
Momoko and Kaoru have great friendship together despite fighting with eachother. For example, when Momoko deemed herself as the leader of the Powerpuff Girks Z, Kaoru did not conform to this, saying the three were equal. Regardless, if one is in trouble , the other will surely attempt to rescue her.
Bubbles has been very nice to Kaoru and as such, Kaoru greatly respects Miyako. Like Momoko, Kaoru began to accept Miyako as more of a friend as time went by and she got to know her better.