Fortress Satsui no Hado

Fortress Satsui no Hado (殺意の波動 Satsui no Hadō, "Surge of Murderous Intent"), sometimes translated as the Dark Hado, is a dark force, that is known for its use by Uryu and Alphamaru.

Description
The Satsui no Hado is a form of ki that is rooted in the darker aspects of the natural human instinct (including the desire to survive, trample, and impose over opposition), and on a metaphysical level, the natural occurrence and manifestation of loss, decline, and destruction.

To tap into the Satsui no Hado, a person must be so consumed with the desire for winning, or else possess such intense rage, that they are willing to murder. As such, only people who push themselves to be the best at any cost can take full advantage of it, however, the untrained mind can be driven into insanity if they are not ready for it.

Physical and Mental Changes
For the people who do succeed in controlling it, they become very strong, but at the cost of losing their humanity and compassion; they develop a cold outlook on life and a nihilistic detachment from themselves, as well as other people, and develop a murderous (and even suicidal) desire to fight.

Such people also gain the power to sense, and potentially influence, the emergence of the Satsui no Hado in others. Once a person has tapped into the Satsui no Hado within them, it can be very hard to resist.

Usage

 * Paul Gekko was once seen meditating while tapping into the Satsui no Hado, so he probably encouraged or at least accepted it, but he did not lose his humanity like Uryu. This is likely because he only used it to a degree, which is why he kept his human facial appearance and did not demonstrate signs of corruption.
 * Uryu fully gave in to the Satsui no Hado, Using the Prototype Transformations. Paul Gekko was actually pleased and somewhat impressed with his Descendant for tapping into Satsui no Hado during a life or death battle for control of their school - or so he thought. wanted to tap into the Satsui no Hado to become far more powerful, and wanted to use it for helping people.
 * Alphamaru vowed to reject the Satsui no Hado, because he knew that he could not control this dark force, and thus could not risk killing anyone he fought or losing his humanity.

Users

 * Paul Gekko
 * Uryu
 * Alphamaru