Koinatsu is a beautiful woman with fair-skin and soft features. She has large but relaxed bronze-colored eyes and small eyebrows with black hair.
She is dressed as an upper classed oiran/tayū having date-hyōgo Nihongami-styled hair with multiple gold-colored hirauchi kanzashi hairpins supporting both the maegami and tabo sections of her hair. She wore an elaborate Susohiki/Hikizuri (trailing skirt) kimono being purple with white polka-dots as its pattern, with a peach-colored haori with multiple golden clouds near the hem and cuffs, and a yellow juban under everything reaching her ankles. She has a pink-sakura colored obi with a Fukura-suzume styled-musubi knot exposed at the front at the front and tall, black three-legged sanmaiba/koma-geta or mitsu-ashi shoes.
Koinatsu is a kind and gracious person, readily thanking her kamuro/shinzō subordinates and awarding them with candy for a job well done, as well as smiling at their happiness. In addition, she worries deeply for their well-being when she was to leave to marry a prospective suitor, especially in regards to her inability to investigate the various disappearances that plagued her district. She is also an observant woman, having known that Tanjiro was a boy from the moment he arrived at her establishment. She also seemed to dislike the spreading of rumors, chiding her subordinates for discussing them with Tanjiro, presumably for misinformation.
Koinatsu was an oiran in the Tokito House. Due to her status, she was one of the most revered people in all of Yoshiwara.
Once, apparently, a very respected man decided to marry her, which she was extremely happy about. After this event, she left home and the Red Light District in general.
As an ordinary human, Koinatsu doesn't possess any additional powers or abilities.
- Koinatsu's name contains the Kun'yomi/reading for both the kanji for "carp" (鯉 koi?) and "summer" (夏 natsu?).