Yūreiyushi

"Yūreiyushi are among the foulest of creatures to inhabit the spiritual worlds... they feed off of a person's happiness until there's nothing left but anger and hate... until you are reduced to something like itself, soulless and evil. They hold no remorse; nor pity, feelings, or mercy. Even Hollows fear to tread on a Yūreiyushi's territory. If it can, it will continue to eat away at your postive traits until are left with nothingness... resulting in a horrible shell of your former self. There's no chance of recovery. You'll just... exist. And your soul will be lost... forever."

- Madara Kawahiru Yūreiyushi (推論のファントム, "phantom of reasoning") are dark creatures that exist within the spiritual worlds. It is said they are corrupted fragments of the Kōtotsu that were sheded off and left to fade away. However, in rare occurances, these fragments fall through a small opening in the Dangai which cause them to fall in a random dimension. They feed off of happiness and thus, leave a victim with nothing but their worst experiences and emotions until they become a hollow shell. They can also suck out a person's soul, which is stored inside the Yūreiyushi in a torrent of screaming souls; presumely other victims that crossed paths with the Yūreiyushi. They hold loyalty to no-one, and have no self of morality, sucking out the soul of any victim that they come across; this applies to little children as well. The most unique thing about them is that they are made of reason, making all spiritual attempts futile as they are completely resistant to all forms of reiatsu and reiryoku. Shinigami are ordered that encountering a Yūreiyushi means retreat; under no circumstances are they to confront the being.

Appearance
Yūreiyushi appear as black spectors, wearing long black robes that end in burnt edges. Their mouths are shown to be sewn together, taking a form similar to a skull's teeth. Their eyes are blue flames, which are assumed to be the souls of their victims. They have a humanoid shape, reaching a height of 10 feet. They are shown to have very long grey fingers, which break away at anything that has spiritual energy.

Powers & Abilities
Depression-Induced Aura: They emit an aura that functions similarly to spiritual pressure, in that greater amounts can frighten those who feel it. However, they mainly cause one who feels their presence to lose all forms of hope and happiness in them.
 * Soonya (शून्य (うつ病ブラ耳をつんざく), sūn'ya; Hindi for "Zero", Japanese for "Deafening Depression Blast") is a burst of reason which can be fired from the mouth of a Yūreiyushi. It is capable of immense destruction, depending on the amount of power put into the attack. It is formed in a way similar to the Hollow's Cero, but is said to appear as a "black burst of dense, solid and thick smoke" when fired. Because it is completely composed of reason, anything that is made of spiritual energy can and will be destroyed when coming into contact with the attack. Like their aura, a Soonya emits a frequency that causes depression in the mind and heart of nearby witnesses.

Immense Speed: Yūreiyushi are shown to be very fast, considering they lack body mass. They move by a strange speed technique that cause them to fade away and reappear in a different location in an instant. They fade away as a puff of black smoke (in contrast to how Seijin Masters apparate as white puffs), which make them untrackable and intangible whilst in that form.

Spiritual Decomposition: Because they are made of reason, spiritual power cannot come into contact with a Yūreiyushi. Spiritual bodies, such as the body composition of Shinigami and Hollows for example, slowly break down into pieces when they are physically touched by a Yūreiyushi.

Soul-Stealing: Yūreiyushi are able to suck out the souls of a victim and those souls are stored inside a Yūreiyushi's body. What's more, when the soul is absorbed inside, the Yūreiyushi is able to utilize the abilities of their victim for the first few hours of the process.

Behind the Scenes
Yūreiyushi are inspired by the Dementors in Harry Potter. They seem to follow a Hindi motif.