Seiatsu

"W-what?! One second it's normal and then it spikes tremendously!"

- Kento Tensei commenting on Koga's "odd" reiatsu

Seiatsu (制圧, Oppression) is a type of Shinigami who's emotions have been animated by the Hōgyoku. There is only one known case in the form of Koga Tensei. They are Shinigami who have gained unique power due to this, unlike that of Vizard or Arrancar.

It should be noted that this transformation greatly resembles Sōsuke Aizen's transformation during the Fake Karakura Town arc, meaning that the two could be related somehow.

Overview
Seiatsu are extremely rare. In fact, it is completely impossible to become one through natural means. It is even impossible to reproduce them via inventions, reiatsu experiments, or even specialized machines. The only known Seiatsu to have ever existed is Koga Tensei.

During a Seijin exploratory mission to Hueco Mundo and after a brutal confrontation with Takashi Sora, Koga's team came under the attack of the Arrancar, Xerxes Averian. In the midst of the attack, Koga's friends arrived to assist him and ends up getting dragged into the attack. Koga's reiatsu begins to fluctuate and, after Seireitou's unconscious form is also attacked, he begins to transform into a Seiatsu. Sora later comments that he had the Hōgyoku on his person during his confrontation with Koga's group, and forced it to obey Koga's desires, unknown to Koga himself. Since Koga was desiring to free Seireitou from his Hollow form at the time this was happening, the Hōgyoku began to act on it until the object found something interesting. It somehow realized that Koga's true desires were to protect all of his friends from harm, because his friends were ever so few. The Hōgyoku also realized that Koga could not do this without another source of power, so it lumped all of his negative emotions together to create an inner being called a Dark Side (暗部, anbu) or more specifically Dark Koga.

Originally, the transformation that resulted from Dark Koga taking over Koga was thought to be Hollowfication, however, Renge Yamato comments that the reiatsu that is produced feels nothing like that of a hollow's. Later, Sora also comments on this. He states that, for some reason, the Hōgyoku used traits from Seireitou's Hollowfied form (which Koga was watching while the Hōgyoku was unknowingly transforming him) in the transformation it was creating; such as a change of hair, hollow eyes, and dual voices.

This process had extremely negative effects on the Hōgyoku; something that was not planned for by Sora and shocked him once he found out. In order to give Dark Koga the power source the Hōgyoku was initially trying to produce, the Hōgyoku transfered it's odd, yet truly immense energy into Dark Koga, forcing the Hōgyoku back into it's dormant state.

Powers & Abilities
Evolving Transformations: Unlike Vizard, who summon a Hollow Mask to utilize thier powers, there is no such thing for a Seiatsu. While Koga is unable to control his Dark Side at the moment, Sora has admitted that there is a possibility to control the form and doing so would make Koga tremendously more powerful. The first signs of a transformation is Koga's eyes turning into that of a Hollow's, black pupils, yellow irises and black sclera, as well as his hair turning dark grey and lengthening slightly. As the transformation progresses, a white liquid erupts from the buckle on his zanpakutō strap and covers his body, hardening in the process. In this new form, he appears as a phantom-like figure. His face is covered with a white canvas and his outfit is now a white cloak that is split in four sections near his waist, similar to coattails. There is a cross in the middle of the cloak, showing where the clip to his Zanpakutō strap is, which is were the substance originated. Also, when he is attacked, his body appears to crack and fold under damage, only bleeding when an attack is powerful enough. This form is eerily similar to Sōsuke Aizen's transformation during the Winter War, only it seems to take place backwards, with the hollow-eyed Human stage coming before the so called "chrysalis form". If the transformation progresses even further, not much changes in his appearance. He begins gaining coattails until he has a total of nine, signifying that his transformation is complete.


 * Enhanced Speed


 * Enhanced Stamina


 * Enhanced Strength


 * Enhanced Durability


 * Enhanced Spiritual Power: Since the Hōgyoku transfered it's unique energy into Koga as the transformation's main power source, Koga now has dual-type spiritual energy which is half Shinigami, half Hōgyoku. Like the Hōgyoku energy, Koga's spiritual power becomes overbearing, unlike anything else in Soul Society, and completely unrelated to reiatsu. His energy increases as his transformation progresses. By the completion of his transformation, his spiritual energy has reached a whole new level. Renge comments that it is the largest amount of spiritual energy he has ever seen in one body.


 * Enhanced Telekinesis: His Seiatsu powers even effect his Shiro Nagare manipulation of his Seijin powers. Of all his new powers, this one is the only one that will remain outside of his transformations. His telekinesis is now deeply linked to his emotions. During flashbacks that prove emotionally painful for him, the outside world is noticeably affected by earth tremors and the cracking and smashing of nearby objects, all caused by telekinesis.


 * Sara (皿, Disc): This technique, named by Dark Koga, creates an energy disk about the size of Koga's palm. The disk can then be fired, slicing through anything it comes into contact with. Koga has also shown the ability to cause the technique to expand in mid flight to allow it to cover a much larger radius.


 * Regeneration Powers: The cloaked form of the transformation has been demonstrated to actively protect Koga by healing his injuries almost instantly.

Behind the Scenes
This race has it's basis in many places. After seeing Aizen's transformation in the manga, I decided to delve into it further by making something eerily similar to it, yet not the same thing. It is loosely based on the Jinchūriki theme of Naruto, and even finds some of it's roots in Hollowfication. Keeping true to the Star Wars theme of the Seijin (which Koga is one of), the "inner being" created by this transformation is called a Dark Side.

Note: This page is only for my use. No one, I repeat, No one is allowed to use this idea or turn there characters into a Seiatsu by any means.