Patchouli Knowledge

Patchouli Knowledge is a witch youkai and the resident librarian of the Scarlet Devil Mansion, appearing from the Touhou Project's 6th title, Embodiment of Scarlet Devil onwards. She's known to be an extremely powerful and experienced magician, due to having spent most of her life researching the countless tomes within the Mansion's library, though this is offset by her poor health.

Character
Patchouli is fairly short, with purple hair and eyes. She has multiple ribbons tied to her hair and other parts of her clothing, and wears pink pajama-like clothing and a night-cap with a gold crescent moon on it. Patchouli isn't a very proactive person, preferring to walk her own path. In fact, the only time she does act in a proactive manner is in the pursuit of knowledge. She's very by-the-book, and is both introverted and silent, in both expression and manner. Patchouli suffers from asthma, anemia and vitamin A deficiency, making her physically weaker than most humans.

Embodiment of Scarlet Devil
Patchouli attempts to stop either Reimu Hakurei or Marisa Kirisame from gettung deeper into the Scarlet Devil Mansion, depending on the player's choice at the start of the game. However, due to her anemia, she is only able to caste up to two elements at a time, and is defeated. Later, when Flandre Scarlet gets out of the basement whilst Remilia is away, Patchouli conjures up rain around the Mansion to stop her from getting out. When the player returns, she challenges them to a second battle, this time with her full power as she is feeling better.

Later Games
Patchouli appears in Sakuya Izayoi's endings for the games Perfect Cherry Blossom, Imperishable Night, and Phantasmagoria of Flower View. In Perfect Cherry Blossom, she shows Remilia how she created a clay model diorama of cherry blossoms. In Imperishable Night, she explains how one would go about creating a vehicle to get to the moon, foreshadowing the events of Silent Sinner in Blue. In Phantasmagoria of Flower View, she comments on the potential poison that could be made using the flowers Sakuya collected to make tea with. She also appears in Subterranean Animisim, assisting Marisa in dealing with the incident and, later, explaining how evil spirits are made.

Bohemian Archive in Japanese Red
Patchouli's article in the novel revolves around her decision to organize a Japanese setsubun festival at the Scarlet Devil Mansion, despite being near the start of summer, rather than the traditional time, between winter and spring. She justifies this decision by claiming that "setsubun" originally means "interval between seasons," and that having the festival at a different time is fine, so long as it fits this criteria. Due to this being an outside-world holiday, she is unclear on most of the details. Aya Shameimaru interviews Patchouli again afterwards, where she says that she was generally happy with how the festival turned out, though she did need to forbid the Fairy Maids from throwing beans around in her library.

Silent Sinner in Blue
Patchouli is the creator of the rocket that Remilia Scarlet, Reimu Hakurei, Marisa Kirisame, and Sakuya Izayoi use to reach the Moon, being the driving force for both the research and design of the craft. However, she is unable to create the rocket fuel, and decides to get Reimu to help by using her powers. She chooses to remains behind as the navigator when the rocket travels to the Moon.

Oriental Sacred Palace
Patchouli is seen stumbling around her library for research materials, before heading to the Hakurei Shrine to recover some books that were stolen by Marisa Kirisame. The book she's looking for had its seal unlocked, but no one knows by whom. In the meantime, the Three Fairies of Light sneak in and take a few books home with them, only later discovering that they're unable to read them.

Abilities

 * Flight - Patchouli is capable of flight, through the use of her magic.
 * Elemental Magic - Patchouli has the ability to manipulate the five elements of Wu Xing - fire, water, wood, metal and earth - as well as the sun and moon elements. She is also powerful enough to combine up to five elements into a single spell, even when the elements are normally opposed to each other. However, due to her poor health, she is usually limited to one or two elements at the most.
 * Magical Books -  Many of the books in the Scarlet Devil Mansion's library are magical in origin. When fighting in the library, Patchouli is able to use these books as a sort of automated weapon, the books casting whatever spells are written in them alongside her own.

List of Spells

 * Fire Sign "Agni Shrine"
 * Water Sign "Princess Undine"
 * Wood Sign "Sylphy Horn"
 * Earth Sign "Lazy Trilithon"
 * Metal Sign "Metal Fatigue"
 * Fire Sign "Agni Shine High Level"
 * Wood Sign "Sylphy Horn High Level"
 * Earth Sign "Lazy Trilithon High Level"
 * Fire Sign "Agni Radiance"
 * Water Sign "Bury In Lake"
 * Wood Sign "Green Storm"
 * Earth Sign "Trilithon Shake"
 * Metal Sign "Silver Dragon"
 * Fire & Earth Sign "Lava Cromlech"
 * Wood & Fire Sign "Forest Blaze"
 * Water & Wood Sign "Water Elf"
 * Metal & Water Sign "Mercury Poison"
 * Earth & Metal Sign "Emerald Megalith"
 * Moon Sign "Silent Selene"
 * Sun Sign "Royal Flare"
 * Fire Water Wood Metal Earth Sign "Philosopher's Stone"
 * Fire Metal Sign "Saint Elmo's Pillar"
 * Earth Water Sign "Noachian Deluge"
 * Metal Wood Sign "Elemental Harvester"
 * First Card "St. Elmo's Explosion"
 * Second Card "Deluge Forty Days"
 * Metal Earth Sign "Djinn Gust"
 * Sun & Water Sign "Hydrogenous Prominence"
 * Water Fire Sign "Phlogistic Rain"
 * Moon Wood Sign "Satellite Himawari"
 * Sun Moon Sign "Royal Diamond Ring"
 * Water Sign "Jellyfish Princess"
 * Sun Wood Sign "Photosynthesis"
 * Fire Sign "Akiba Summer"
 * Moon Metal Sign "Sunshine Reflector"
 * Fire Water Sign "Phlogistic Pillar"
 * Earth Metal Sign "Emerald Megalopolis"
 * Fire Sign "Ring of Agni"

Trivia

 * Patchouli has earned the nicknames "One-Week Wizard" and "Wizard of the Week" with fans, for her secret hobby. In Japan, the days of the week are named based on certain elements, the same elements Patchouli uses for her spells. As such, she takes pleasure in making sure her spells match with their corresponding days.