The Impure King (不浄王 Fujō Ō) is an exceptionally strong decay Demon, and is the sworn enemy of the Burning Impurity Kongo, Ucchusma. It is classified as kin of Astaroth and seems also to be related to the Impure Princess.
140 years in the past, during the last days of Edo and in the fifth year of the Ansei Era, the Impure King is said to have spread a plague of miasma, decay and fever that killed over 40,000 people. A monk named Fukaku used the fire demon Karura in combination with the sacred sword Kurikara to suppress the Demon and removed its Heart, splitting it into two halves as proof of having subdued it, which would come to be known as the Impure King's "eyes".
The body of the Impure King was hidden away beneath the Myōō Dharani sect's original headquarters, while the left and right eyes were sealed away in the True Cross Academy's Saishinbu and the Kyoto Branch Office, respectively.
Kyoto Impure King arc
In present time, both the Left Eye and Right Eye are currently being held under the surveillance and possession of the True Cross order with the help of the Myoda sect. Saburota Todo, having stolen the Left Eye, manipulated Mamushi Hojoof the Myoda sect into stealing the remaining Right Eye for him, allowing him to implant them both into the previously sealed body of the Impure King at the Goma-do (Devil Conquering Shrine), reviving it in the process. Before Todo could return the eyes Tatsuma Suguro arrived and revealed his familiar Karura, a fire Demon that holds a contract with the descendants of the high priest Fukaku. Even though he was able to put up a good fight, Todo distracted Tatsuma and was able to return the eyes to the husk of Impure King, reviving the demon.
As the Impure King began to grow in size, Tatsuma used Karura to seal the demon with its flames, but it left him fatigued and allowed Todo to stab him the neck from behind. Revealing his plans, Todo forcibly absorbed Karura by swallowing it, physically empowering him. With Tatsuma mortally wounded, the Impure King was freed and began growing to a massive size and spreading its fungi across the mountain eventually taking on the shape of a castle and preparing a sporangium at its core.
Powers & Abilities
According to legend known only to the High Priests of the Myōō Dharani sect the Impure King will steadily grow larger until it reaches the size and shape of a castle. Within its core it will form a sporangium that when matured, bursts and releases a dense cloud of toxic Miasma, that Mephisto Pheles likens to a natural disaster. The Impure King spreads fungi while growing that steadily grows and engulfs anyone trying to combat it.
As kin of Astaroth, the Impure King is weak to fire and it can be used to combat its spreading fungi, but the only way to kill the Impure King is to destroy its core that is within the center of its sporangium.