Wisteria

Wisteria is a plant predominantly used by the Demon Slayer Corps to combat demons.

History
Sometime in the past, a family was saved from demons by the Demon Slayer Corps. To express their gratitude, the family designed their family crest with a wisteria flower so Corps members would be able to identify the home, and stay there free of charge.

Shinobu Kochu primarily uses poison made with wisteria to battle demons, as she lacked the physical strength to behead them. To achieve this, her sword is shaped in such a way that it will inject a dosage into a demon through her Insect Breathing forms. Her sheath houses a supply of poison to keep her blade poisonous.

During Tanjiro's Final Selection, it is revealed that wisteria growing around the base of Mount Fujikasane is what imprisons demon inside to use as a test for would-be Demon Slayers.

Uses

 * During Final Selection, wisteria is used to keep the Demons trapped on Mount Fujikasane, hence the name "Fujikasane," which translates to "covered in wisteria".
 * Following the Final Selection, wisteria is used to engrave the ranks of the corps members on the back of their hands.
 * Wisteria can be used to create poisons which can paralyze regular Demons and immobilize Lower Ranks of the Twelve Kizuki. In high enough concentrations, as used by Shinobu Kocho, these poisons are shown to be capable of dissolving almost any demon, negating their regeneration powers.
 * With the help of Tamayo and Yushiro, Shinobu was also able to utilize wisteria poison in modifying her own body. In preparation against Doma, Shinobu willingly altered her own physiology so that every single cell of her flesh was laced with poison, with her body effectively becoming a undetectable, human poison capsule that would slowly destroy the body of even the highest Upper Ranks of the Twelve Kizuki with enough time once they devour her. As stated by her, with her bodies overall size and and body weight, she is 37 kilograms worth of poison, approximately seven-hundred times more than the lethal amount needed to kill an average demon.
 * Wisteria is used by Shinobu to create a medication which would turn a demon back into a human.