Ansatsuken

Ansatsuken (lit. Assassin's Fist) is a dark martial art practiced by Ryu. It, like Hokuto Shinken, was designed primarily as an "assassination art", with the sole intention that its practitioners would kill their opponents. Katniss studied the art under Ryu, but after an unfortunate mishap, decided to never use it again. Except the leg sweep.

Basic Principle
Ansatsuken is primarily focused on the manipulation of ki energy in quantities large enough to be used for ki projection attacks. In order to do so, users tap into a mysterious force known as the Satsui no Hado (lit. Surge of Murderous Intent), which focuses all of their willpower on killing their opponent. This focus makes a large amount of ki readily available, perfect for the explosive moves utilized by the style. However, the Satsui no Hado is a double-edged sword- it can consume the user, impressing the desire to kill upon them and driving them insane. It takes years of mental training to learn to suppress these urges... something Katniss did not have the advantage of when she learned the art.

Techniques

 * Tatsumaki Senpukyaku (Hurricane Kick)- The user leaps into the air and delivers a set of laterally-spinning kicks before landing. Katniss' variant, called the Shinrin Kasai Kyaku (Forest Fire Kick) only used two strikes, but was highly effective. Sol Badguy uses a similar technique called the Bandit Revolver. 


 * Shoryuken (Rising Dragon Punch)- The user leaps into the air while twisting their body and extending their striking hand, delivering an uppercut that lifts their opponent into the air while striking them multiple times. A small amount of ki can be used to enhance the attack further, resulting in a Shin Shoryuken. Katniss used a high-powered, ki-charged variant called the Shohiken (Rising Blaze Punch), which always creates a small trail of flames and was powerful enough to kill Tris Prior. Morrigan uses a similar technique called the Shadow Blade, which we're certain is an innuendo.
 * Hadoken (Wave Motion Fist)- Ansatsuken's most powerful technique. The user channels ki into their hands and collects it into an orb, which they then project forward. The fiery orb flies towards its target in a straight line and explodes, dealing great damage. Ryu has several increasingly-powerful versions of the Hadoken, including the Shakunetsu Hadoken and the Shinku Hadoken. It was not easy for Katniss to attune herself to the Satsui no Hado enough to perform a Hadoken, but after witnessing Holly's death was able to channel the immensely powerful Suzaku Hadoken (Vermillion Bird Wave Motion Fist). The Suzaku Hadoken was a small, fast-travelling orb of energy that expanded on contact with its target into a devastating spherical explosion. Eventually, Katniss gained the ability to fire a normal Hadoken as well. Morrigan uses a similar technique called the Soul Fist, a small, bat-winged orb of energy that explodes against its target. The Soul Fist does not seem to have the raw power of most Hadokens, however, but Morrigan can throw them much more rapidly. Now that's got to be an innuendo.
 * Shin Shun Goku Satsu (True Instant Hell Murder)- an attack only available to those fully consumed by the Satsui no Hado, expressly forbidden from use by the art's grand masters. It is unclear exactly how the technique works. The user grabs their opponent, who descends into a mysterious darkness, dying shortly thereafter. No one who has observed the move first-hand can ever remember the details, but they're probably horrifying. The attack has a tendency to burn cool and foreboding kanji onto the outfits of its user. Katniss used it to kill her father for the second time, signalling her consumption by the Satsui no Hado.
 * Ashura Senku (Ashura's Flashing Air)- A technique only used by those consumed by the Satsui no Hado. The user can float just above the ground a short distance, allowing them to dodge attacks even at point-blank. It requires a great deal of coordination. Katniss used this technique extensively during her battle with Ryuko, in order to negate her speed disadvantage.
 * Kongou Kokuretsuzan- An attack only available to those fully consumed by the Satsui no Hado, the user charges ki into their palm and strikes the ground, creating an explosion of deadly energy waves. Katniss used it against Ryuko, to little effect.