Satsui no Hado

The Satsui no Hado (殺意の波動), sometimes translated as the Dark Hado, is a dark force, that is known for its use by Akuma, as well as Ryu's struggle against it.

Appearances
The Satsui no Hado made its debut during the first World Warrior Tournament, where Ryu unknowingly awakened something inside of him to defeat Sagat in a drastic effort.

Originally, Ryu scarred Sagat with a single Shoryuken. It was later retconned in Street Fighter Alpha that Ryu lost control of himself and his rage by rising up fist first, scarring Sagat with a Metsu Shoryuken instead. His attack took on the properties of Goutetsu's original art, despite having never been taught it by his master Gouken. Although Sagat wanted revenge for his scarred chest, he never knew that the scar came from something that had awakened the darkness inside of Ryu until the events of Street Fighter Alpha 3.

Description
The Satsui no Hado is a form of ki that is rooted in the darker aspects of 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. Learning the Satsui no Hado is the first step in learning the most fatal technique known to all of their martial arts - the Shun Goku Satsu, known also as the Raging Demon.

Physical and Mental Changes
For the people who do succeed in controlling it, they become unbelievably 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 almost 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. Within the main storyline, Goutetsu is the only one known to date that was able to utilize its power without completely giving in to its murderous and darkest urges.

When under the Satsui no Hado's influence, a person's eyes willl glow white and red and gain sharp fangs. If one embraces it to a lesser degree, their eyes will glow blue. If one has used it to their fullest extent for too long, they will transform into a demonic being, likely one similar to Oni.

Goutetsu
Goutetsu himself 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 Akuma. 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. This was also how both his students Gouken and Akuma were introduced to its power.

Goutetsu would also have had to teach them about the Satsui no Hado to his pupils if he did teach them the Shun Goku Satsu, but Ryu (only under the influence) can also use this move despite the fact that Gouken never did teach him the move, meaning that the move is an inherent quality of the dark power.

Akuma
After Akuma fully gave in to the Satsui no Hado, he lost all of his humanity, as well as his compassion as a person, to the point of becoming a demon who only seeks a battle that will cost him his life towards another warrior, and a person that only wants more power, taking a demonic appearance to match his darkend soul.

Goutetsu was actually pleased and somewhat impressed with his student Akuma for tapping into Satsui no Hado during a life or death battle for control of their school - or so he thought. Akuma wanted to tap into the Satsui no Hado to become far more powerful, and wanted to use it for killing people who he found worthy of killing, rather then using it for enlightenment and good like Goutetsu. Goutetsu may have been unaware that his student had lost all of his humanity and his compassion as a person.

However, Gouken, a student of Goutetsu who taught a toned-down derivation of the style by removing the dark power, detested the Satsui no Hado, as he believed it encouraged killing after seeing how Akuma used it to murder Goutetsu. He condemned his brother Akuma for corrupting his Chikara no Hado (力の波動) and vowing to never teach it to anyone.

Although Akuma may have tamed the Satsui no Hado, he could not stop the side effects of this dark force, although it is highly likely he had no desire to. His understanding of the Satsui no Hado is so great that he can embrace it to a much lower degree, giving lesser opponents a fighting chance. However, he still cannot return to his human self, as he has completely lost his humanity, and has used it to his fullest extent for too long.

Oni
Oni is the result of Akuma fully 'merging' with the Satsui no Hado. As explained earlier, his appearance has changed to that of a larger, demonic being, with a supernatural power beyond that of Shin Akuma.

Evil Ryu
During Street Fighter Alpha 2, Ryu finally realized that the Satsui no Hado was the culprit behind his aforementioned victory over Sagat. Ryu 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.

Although Ryu never shows any signs of the Satsui no Hado's influence after the events of the Street Fighter IV series, several games present a hypothetical version of Ryu who has embraced the power, willingly or not, becoming Evil Ryu. Furthermore, other media often depicts him temporarily succumbing to the Satsui no Hado and assaulting an opponent before returning to normal.

It was not until the end of Street Fighter IV that Gouken was able to seal it away using the "Power of Nothingness" to help him control it like Goutetsu; however, it is unknown how long the seal will be able to hold his dark power. A demonic version of Evil Ryu appears in the Arcade Edition of Super Street Fighter IV with a redesign and a more powerful boss form, possibly to show how he would transform if the seal was broken.

In addition, Ryu and Ken's ending in the crossover Street Fighter X Tekken suggest that Pandora's power is trying to influence, and merge with the Satsui No Hado within him.

Dan Hibiki
In the events of UDON's Street Fighter Legends: Sakura miniseries, Dan falls to the dark power while fighting Sakura. However, Dan's attempt to perform the Shun Goku Satsu on her fails by resulted in him tripping over her backpack and rendering himself unconscious by Sakura's attack.

Dan has a different kanji appearing on his back, showing the kanji (父). It is possible Dan's power stems from the feelings of hatred that he harbours towards Sagat for murdering his father.

Sakura Kasugano
In Marvel Super Heroes vs. Street Fighter, there is a secret character known as Dark Sakura (also called Sunburnt Sakura), a version of Sakura who utilizes a mixed moveset of Akuma and Evil Ryu. Unlike Ryu and Akuma, Dark Sakura is able to control her powers, and her personality remains mostly unchanged. This also makes Sakura the only female to have used the Satsui no Hado at any point.

Known victims of the Satsui no Hado

 * Goutetsu - Killed by Shin Akuma in a honorable fight to the death.
 * Sagat - Scarred and defeated by Evil Ryu's Metsu Shoryuken accidentally.
 * M. Bison- Defeated and seemingly killed by Akuma's Raging Demon in Super Street Fighter II Turbo.
 * Gill - Defeated and seemingly killed by Akuma's Raging Demon in Street Fighter III, but recovered via resurrection.
 * Shun - Killed by Evil Ryu during the events of Street Fighter Alpha: The Animation. (Alternate Continuity)

Trivia

 * While Kairi from the non-canon Street Fighter EX games is not a user of the Satsui no Hado, the power he wields works in a similar fashion.
 * The being Garuda, is also said to be linked to said power in the EX games.
 * In the iOS game Street Fighter IV Volt, the Satsui no Hado appears as a skill in Wandering Warrior. However, one would need the title "Messatsu!" to get this skill. When this skill activates, the player's avatar endures the hit that would have cost the avatar the match with 1 HP remaining, and then, it activates. While this skill is active, the damage the player's avatar scores on the opponent's avatar is increased.