Satsui no Hadou, literally "Surge of Murderous Intent", is one of the several Super-Natural elements of the Street Fighter series. It is a power based in traditional Ansatsuken teachings that can be unlocked in a few special people born with the potential for it, but to unlock it, the fighter must do away with any kind of compassion for their fellow man. To tap into the power, a fighter must want to win with such fervour that he is willing to kill his enemy. The downside is that an untrained mind could be driven insane by the overwhelming power that this technique allows the user to have, or killed outright from the raw power. Those that do manage to tame it gain a cold outlook on life, with disregard for humanity. As the only man to become one with Satsui no Hadou Akuma is considered a master and as a result is often referred to as a demon.
The most famous technique of the Satsui no Hadou is the Shun Goku Satsu, or Instant Hell Murder/Raging Demon, which in the games is typically a super move for Akuma. The move itself has never been explicitly shown in any fighting game, as when it is performed the screen goes dark and the sound of several attacks and screams of pain from the victim is the only observed part of the attack. Typically, If the move results in a K.O. of the other fighter, a loud screeching noise is heard, and the screen flashes with the giant kanji "Ten" (heaven, enlightenment), the same kanji featured on Akuma's back.
Goutetsu is the first character in the Street Fighter fiction that is known to be a practitioner of a deadly martial art intended to kill, teaching the skill to Akuma and Gouken.
Originally, the hit that scarred Sagat's Chest was a plain Shoryuken, but that was later changed to Ryu unknowingly tapping into the Surge of Murderous Intent. Ryu's hatred for Sagat allowed him to tap into the power without ever even being taught its methods by Goutetsu. Ryu later would struggle with it as depicted in Street Fighter Alpha: Generations. Also it would be the assumed justification for the alternate reality character "Evil Ryu".