Outside of the band, she is also Chisato's childhood friend, and their parents are good friends as well.
Kaoru is a tall girl with angular facial features, slanted crimson eyes, and long purple hair worn in a ponytail. She has chest-length forelocks and bangs that frame her face with a single lock that hangs loosely between her eyes.
Her casual attire is normally boyish and formal. In her initial casual wear, Kaoru wears a high-collared white shirt with a black vest on top of it, black vertically striped loose pants, and a pearl necklace as a finishing touch.
During winter Kaoru wears a gray sweater with white stripes at the top and bottom, a black loose scarf around her neck, and white jeans. During summer she wears a white front tie shirt which has black flowers on the left side, a blue shirt underneath, and high-waisted jeans with a brown belt. Her outfit is completed by a thin chain necklace.
When she was younger, her hair reached only up to her shoulders; after middle school, she started growing it out.
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's 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. Her catchphrase is "fleeting" - though when Hagumi or Kokoro questioned her about what it meant, Kaoru could not answer.
Despite appearing to be very prideful, Kaoru struggled with self-esteem problems in the past and created her princely persona to flatter other girls so they may never feel the same way. She also used to be shier and lamented the fact that she was not strong enough to protect Chisato from their classmates believing she was an evil and mean person because of one of the roles she acted in.
A list of characters Kaoru interacts with in the game (during Lives and in the dialogues at the end of every game).
Seta (瀬田): Se (瀬) means "rapids, current" and Ta (田) means "paddy, field".
Kaoru (薫) means "fragrant, scented".
- She, together with Tomoe, are known as the two most popular girls in Haneoka.
- Kaoru is part of her high school drama club with Maya and has been acting in theater productions since middle school.
- She also hosts a corner called "Shakespeare with Seta Kaoru" in the broadcasting room during lunchtime.
- Kaoru used to call Chisato "Chi-chan" when they were younger and is actually really embarrassed about that.
- In return, Chisato calls her "Kao-chan". Kaoru gets flustered whenever Chisato calls her by that nickname.
- She has the same height as Masuki, and is also the tallest member of Hello, Happy World!
- Kaoru is scared of both heights and scary things.
- Kaoru has mentioned that she is quite athletic and that her favorite sports are fencing and horseback riding. She has been shown to be quite skilled in the latter.
- Kaoru's theatrical, princely, and flirty personality is a rather open parody of the anime otokoyaku, that is, the anime and manga heroines, inspired by playing male characters actresses from the all-female Takarazuka Theater. It is also emphasized by her close friendship with the very feminine Chisato, who can be compared to musumeyaku, actresses who perform female roles in the same theater.
- This also justifies her popularity with other girls, because Otokoyaku is embodied by the metaphorical image of the "ideal man" who can be simultaneously considered as a charming handsome prince and a reliable female friend who understands women's experiences.
- Kaoru is the only character in the game who has been seen with more than one guitar. Her cards, as well as their chibis in the game, show her posing with at least 3 different guitars.
- She is also the only guitarist to use semi-hollow and hollow-body guitars, rather than the full-body instruments the others possess.
- In the Ojamajo Doremi collaboration, her design is based on Segawa Onpu.
- Main Story Chapter 8
- Shadows of Days Past Remain/Event Story
- My Former Nickname/Card Story#Special Episode
- A Rose's Name in a Transient World/Event Story
- GARUPA☆PICO Episode 6
- The Cursed Well and the School Spirit/Event Story
- A Fleeting Performance/Card Story#Episode
- In-game dialogue: "I'm quite good at sports. I particularly enjoy horse riding and fencing."
- Summer, Slow Summer/Event Story