"Come hither, devils, to the garden of knowledge. If you each gleam one truth, the whole world will become an open book." Patchouli Knowledge is a magician who dwells in the Scarlet Devil Mansion's library with Koakuma, her familiar... They would very much like to read that book of yours.

Knowledge is a collection of subjective memories of facts that can be recalled at will. It's often said that knowledge is meaningless unless you have the wisdom to apply it, but that's needlessly pedantic. Trying to argue that knowledge is better than wisdom or vice versa is pointless since one's overall level of intelligence is determined by how they work together. Nevertheless, you can't be intelligent without knowledge. Generally speaking, the more knowledge you have, the more intelligent you are. It's like how the size of your muscles determines your physical strength. "Ignorance is bliss" is an empty platitude spoken by weaklings who abandoned the continual pursuit of knowledge and self-improvement. Following that thought, perhaps there was a smarter way to explain all of this...

The word "magician" can refer to human practitioners of magic and a species of youkai. Patchouli is the latter. However, "youkai" is a broad term that encompasses all non-humans, including devils. Some even argue that youkai magicians are a type of devil. "Magic" is the force that causes magical phenomena to occur as well as the term used to describe the methodologies or spells used to harness and direct this force. Put another way, magic is what lurks within the primordial darkness beyond the parts of the universe enlightened by civilization and science. Magicians aren't the sole purveyors of magic. However, unlike other youkai, they spend their entire lives studying and experimenting to formulate and perfect their own magical methodologies.

Learning new things advances civilization. Thus, human intellectual pursuits generally don't mesh well with magic. Science is all about understanding the mechanisms and laws of the universe and how best to exploit them. When denizens of material civilizations see an apple tree, all they think about is how to pull the apples off. The wisdom of magicians lies in their ability to attain knowledge of the unknown without revealing any of the mysteries. Unlike material civilizations, where science is used to develop and grow one methodology shared with as many people as possible, there are as many magical methodologies as there are magicians. All magicians interpret magic differently, which is reflected in the spells they create. The individual nature of magicians resembles the many-worlds interpretation that some outside-world scientists advocated for in the past.

Patchouli specializes in spirit magic, also known as elemental magic. Spirits in this context refer to beings, similar to fairies, that embody elemental forces. However, some claim that these elemental spirits and fairies are one and the same. Or that they're juvenile fairies. Either way, fairies are physical manifestations of Mother Nature, so there must be some connection. Denizens of spiritual civilizations and those well-versed in magic see temperament as the fundamental building block of the universe. Everything from ice and light to swallowtail butterflies is composed of temperament, and the philosophical concepts of the Three Essences, Four Seasons, and Five Phases are used to explain these compositions. An infinite amount of knowledge must be gathered and processed to catalog and describe every temperamental composition in the universe. That's why Patchouli needs an infinitely expanding library.