Seta Kaoru is a third-year student at Haneoka Girls' High Schooland the guitarist of Hello, Happy World!. She is very popular with ladies, whom she dubs her "little kittens". Himari and Rimi in particular have a tendency of blushing in her presence. 

A flamboyant actress, Kaoru has an extravagant personality. She is rather pretentious and bombastic, having a tendency to use impressive sounding words to the point of sounding foreign and hard to understand. She sees herself as a prince, and sees other girls as the princess while quoting Shakespeare or other philosophers (sometimes incorrectly). She appears highly flirtatious, and is very popular among other girls, not only for her passionate mannerisms, but because she is also surprisingly reliable. If she is aware someone may be in a bad mood or feels sad, she will try to encourage them or help them feel better.

When by herself, her "quirks" seem to lessen, if not vanish entirely at times. She appears to be aware of how she can come off to others; sometimes she struggles to have time to herself due to having so many fans, and is aware that she likes certain things that don't fit her "character". She is even able to increase her actress personality if she feels it is necessary.

Though she appears very intelligent, she can often be just as airheaded as Kokoro and Hagumi - such as mistakenly assuming the philosopher Friedrich Nietzsche was a woman, or repeatedly attempting to push on a door that can only be opened by pulling.[1] Her catchphrase is "fleeting" - though when Hagumi or Kokoro questioned her about what it meant, Kaoru could not answer.