|“||Read your mind? I've already closed my satori eye. Reading people's minds only make you depressed and there's nothing good about it.||„|
|~ Koishi Komeiji|
Koishi wanted to avoid the hate and dislike which Satori experienced due to her mind-reading abilities, so she sealed away her own Third Eye. This backfired, since she gained the ability to read and manipulate people's subconscious, an even greater ability. However, she also became much more carefree as a result, and didn't mind as much.
She now spends much of her time wandering the world aimlessly. After her encounter with the heroine in Subterranean Animism's Extra Stage, however, she became curious, and wanted to start actually meeting people.
After the events of Symposium of Post-mysticism, Byakuren Hijiri solicited Koishi into her faction as a laywoman.
In Hopeless Masquerade, she participates in a battle for popularity between Gensokyo's most prominent adherents of Shinto, Buddhism, and Taoism, for fun. It is revealed that, during and after the events of the game, she found Hata no Kokoro's mask of hope and decided to keep it for herself, temporarily obtaining the emotion of hope.
Koishi's presence cannot be "felt" by anyone unless she has entered their direct field of vision, and is forgotten as soon as she leaves it. In general, she doesn't have a personality. However, children enjoy her presence as one of an imaginary friend, whom they forget about once they grow up. However, as Satori's presence has been made known, even Koishi has begun to be recognized as of late.
- (Touhou 11, 12.5) Has wavy, grey-greenish, short hair and dark green eyes, wears a black hat with a yellow ribbon around it. A closed, dark blue "third eye" is positioned over her heart, with cords wrapped around her torso and attached to each of her ankles. Wears a yellow shirt with diamond-like blue buttons and dark green collar. The skirt is also green with a faint flowery pattern, but a lot lighter. Her socks are black.
- (Touhou 13.5) Same as above, except her hair is bright green with yellow shine and it is slightly shorter. Her third eye and its cords are now dark purple and her socks are dark blue.
Koishi wanted to receive the blessing of Kanako Yasaka so she could give her own pets power like Satori's pets were given, so Koishi does apparently have pets. During and after the events of Hopeless Masquerade, Koishi now possesses the original Mask of Hope that once belonged to Hata no Kokoro before she lost it. Koishi found it while wandering around Gensokyo, and because of this, she temporarily obtained the emotion of hope.
- Satori Komeiji (Older Sister)
- Rin Kaenbyou (Sister's Pet)
- Utsuho Reiuji (Sister's Pet)
- Hata no Kokoro (Enemy)
- The characters for Komeiji literally mean "ancient and pure/bright earth". Koishi is not written in Kanji, but it's supposed to mean "love" or "beloved".
- In Koishi's profile, it is said that she met a human at the shrine at the top of the mountain who made her regret closing her third eye and want to learn more about this human. Though it may seem like this was talking about Sanae, once put in to context by the extra stage of Subterranean Animism, it is clear that the human it was talking about is either Reimu or Marisa.
- After the fight with the heroine, she starts to become curious about the Human race and begins to investigate them. The Humans can't see her because of her ability to control the Subconsious. (She uses her ability to become invisible to humans).
- Koishi's musical theme, Hartmann's Youkai Girl, may refer to Eduard von Hartmann (whose most famous work is entitled The Philosophy of the Unconscious) or Heinz Hartmann (as many of Koishi's spellcards seem to make references to ego psychology.) The track itself is also arranged so that it has symmetrical parts, making it sound remarkably similar to itself even when played reversed, possibly as a reference to the practice of backmasking.
- Satori and Koishi's design may have been inspired by the 1939 painting by Kahlo titled "The Two Fridas". The subject is essentially two identical women (sisters/clones/twins...) with visible hearts and external arteries that seem to connect and wrap around their shoulders and arms, where one of them has a cut artery and a pair of scissors in hands (Resembling Koishi, who has closed her third eye).
- If her and Satori's color schemes are inverted, they will both somewhat resemble each other.