Yōkai (YI Arc)

Yōkai were an Organization of powerful and ancient Spiritual entities that desire the destruction of the Balance between the Living World and Soul Society, originally Eight members of Soul Society that had aspirations of overthrowing the Soul King but upon their defeat were imprisoned in Hell and then made a deal with the Destroyer Deity, the Yōkai are the enemies of all living things and do care not for Sōsuke Aizen's conflict with Soul Society.

Overview
The Yōkai are an organization of at least eight members that each had a traumatic fate during their lives, each of them became damned because of their actions however they gained contact with a an ancient Deity who promised them vengeance against the Soul King and Soul Society, their goal was to destroy the balance between the Spirit World and Human World and thus forcefully slam open the doorway to the Soul King's Palace.

Eight Yōkai Emperors
The Eight Yōkai Emperors are the rulers of the Yōkai and the only eight introduced in the series thus far, they are devastatingly powerful and seek to defend themselves and the world they currently live in, few remember or can accept their own pasts.

Past Lives
Each of the Eight Emperors including Maoh himself have a past life in which a traumatic event caused them to fall into Hell and have some connection to the Soul Society Civil War, the past lives are:


 * Maoh was originally the first Soul King whom wanted to create a Paradise for all Souls, however this in turn caused his own people to usurp him given that it would cause imbalance, he was usurped and fled to Hell which over time corrupted his god-like powers and vengeful personality into that of a Destroyer God.
 * Venku was the Prince of Soul Society, adopted by the second Soul King when his parents died when the first Soul King defended himself and raised with all entitlement and training that a Prince of Soul Society deserved, he led a coup against his "father" and became insane before falling into Hell where he was made a deal by Maoh for revenge.
 * Eiyū was a loyal Knight of Soul Society and a high ranked member of an unspecified Division, curious in the goals of the first Soul King and Venku's claims to continue it, he joined Venku's faction in the Civil War but died in battle only to reawaken in Hell.
 * Mahō was the heiress of the Ryōdoji Family and a political ally of Venku during the Civil War, not one to sit on the sidelines she fought alongside her elder brother, but died in battle only to reawaken in Hell.
 * Tsuyo was the greatest Gladiator in Soul Society and a member of the 11th Division, enjoying a fight he often was the lover and rival of the Prince and they fought in the arena however he was framed by the Prince's advisers and raised against by the entirety of Soul Society via the advisors' manipulations for starting the Civil War, despite his shouts of innocence and the Prince defending him he was beheaded and awakened next in Hell.
 * Shisai was the very first Visored and a tamer of Hollows in which he believed that a form of peace could be brought between the two species, however his usage of hollow powers and his consorting with Hollows and Venku's rebels caused him to be branded a traitor, he died defending a Dragon-like Vasto Lorde which awakened with him in Hell.
 * Shogun Kenpachi was the Captain of the 11th Division during the Soul Society Civil War and came into an alliance with Venku's faction becoming a Warlord, he caused many victories and spread the wealth of his victories to the common people however this upset many of his followers, his Lieutenant betrayed and killed him before starting the Kenpachi tradition among the Captains and Shogun then awoke in Hell with the urge for vengeance.
 * Ken was the short tempered member of the Royal Guard and the older brother of Mahō who was the heiress of the Ryōdoji Family, he was charged with being Venku's bodyguard and his loyalty to his brutal lord carried him on into the Rebellion, he died beside his sister giving Venku time to retreat from a battle and awoke with her in Hell.
 * Ōkami was a member of the Shihōin Clan and spied on Soul Society during the war, he was found out and killed many of the Onmitsukidō with his expert usage of high-speed Hakuda, but eventually he was killed among those he had killed and awakened soon afterwards in Hell.

Powers

 * Kyomu Blasts - Literally "Nothingness Blasts", are the equivalent to a Hollow/Arrancar/Visored's Cero and notably far stronger than either versions, it is capable to disintegrate countless Hollows and Pluses with a dismissive blast, the Kyomu Blasts legendarily are used to collect spiritual energy and particles by utterly destroying a spirit and in turn upsetting the balance.
 * Immortality - Although a Yōkai can be mortally wounded and killed, their bodies are not destroyed and can be retrieved, once retrieved and placed into a Yōkai Crystal they can eventually recover and resurrect over a long period of time.
 * Durability - Yōkai are impervious to most natural forms of human pain, being physically harmed by hand-to-hand combat has little to no effect upon them, it takes a powerful blade infused with high spiritual energy to cut into them.

Weaknesses

 * Living World field - Yōkai are limited by the Living World and cannot appear as their true forms in this world, they can however take a human form which - unknowingly to them - is the form they had prior to becoming Yōkai, however the field generated by living beings can be overlooked when a Yōkai is in an extremely dense area of Spiritual energy or when they are in an artificially generated Yōkai Spirit Field. Apparently, for unknown and unspecified reasons, only Eiyū and Maou appear to be exceptions to this rule.
 * Yōkai Jueru - The Yōkai Jueru are bracelets and necklaces that are embedded with a Yōkai Crystal that allow a Yōkai to transform between a Human and Yōkai forms, in Yōkai form these crystals appear to be embedded upon their true forms, if damaged then even Eiyū would be forced back into his human form and trapped that way until the crystal repairs itself.

Trivia

 * In Japanese myth, Yōkai are supernatural monsters dubbed as: "ghosts, phantoms, strange apparitions".