As stated by Gatz, this fighting style allows the user to control vibrations around their limbs to generate shock waves. This shockwave is powerful enough to destroy a metal shield or defeat a strong man easily. Sai also claimed that these attacks are unblockable and reverberating, causing defenses to shatter.
The only drawback is that the shockwaves can be countered by a significant amount of force, as Sai's shockwaves were countered by Ideo's explosive punches, and Chinjao's every shockwave was countered during his fight with Luffy in Block C.
This fighting style can be utilized on any limb of the user's body, whether it be the head, fists, legs, or elbows.
As the 12th head of the Happo Navy, Chinjao has complete mastery over the Hasshoken techniques. His usage of the style is focused on his head, particularly taking advantage of the drill-shape.
Buto (武頭,Butō?, literally meaning "Military Head"): Chinjao jumps in reverse and headbutts the enemy. The strike is strong enough to stop Cavendish's Durandal and creates a shockwave while clashing. It was first seen used against Cavendish in Corrida Colosseum. It is unknown if he uses vibrations in this attack. This is called Head-Arms in the Viz manga and FUNimation adaptations.
For the chapter titled "Open Chinjao", see Chapter 719.
Hasshoken Ogi: Kiryu Kirikugi (八衝拳奥義 錐龍錐釘,Hasshō-ken Ōgi: Kiryū Kirikugi?, literally meaning "Eight Impacts Fist Secret Technique: Drill Dragon Drill Nail"): A secret Hasshoken technique that Chinjao was able to perform thanks to his drill-shaped head. Chinjao hardens his head with Busoshoku Haki and headbutts the target. It was strong enough to split open layers of ice that not even fire or axes could breach, and was the "key", his Open Chinjao (開けチンジャオ,Hirake Chinjao?), to Chinjao's treasure. After his head was flattened by Garp during their duel thirty years ago, he lost the ability to perform the attack. After his head was reshaped by Luffy's Gomu Gomu no Thor Elephant Gun, he regained the ability to use this technique, and was shown using it in combination with Elizabello II's Light Version King Punch to shatter Pica's stone statue arm. However, he lost this ability again when he tried to attack Baby 5 and Sai broke his head to protect her. It is unnecessary to open Jewel Sheet Ice with this technique anymore because this technique passed to Sai. This is called Hasshoken Secret Art:Drill Dragon Nail in the Viz manga and the FUNimation adaptations.
Hasshoken Ogi: Mukiryu Mukirikugi (八衝拳奥義 無錐龍無錐釘,Hasshō-ken Ōgi: Mukiryū Mukirikugi?, literally meaning "Eight Impacts Fist Secret Technique: Drill-less Dragon Drill-less Nail"): After Chinjao's head was flattened and he realized he could no longer open up the ice above his treasure, Chinjao renamed his technique. It was seen in this form during his fight with Luffy in the Corrida Colosseum, with the intent to kill the young pirate. Like the original technique, Chinjao hardens his head with Busoshoku Haki and headbutts the target, but the power is greatly diminished. Although it lacked the characteristic concentric circle vibration lines of other Hasshoken techniques, Chinjao still referred to it as a Hasshoken technique. It became obsolete once Chinjao's head was restored to its drill-shape. This is called Non-Drill Dragon Non Nail in the Viz manga and FUNimation subs. In the FUNimation dub of Episode of Sabo, this is called Hasshoken Secret Art: Non-Drill Dragon Non Nail. In the FUNimation dub of the main series, this is called Hasshoken Technique: Non-Drill Dragon Non Nail.
Buto Kaiten (武頭回転,Butō Kaiten?, literally meaning "Military Head Spin): Chinjao plants his head into the ground and does a head stand, put his hands together and legs apart, and spins like a top. He then moves towards his opponent like a tornado. The force of the attack sent all of the unconscious gladiators around him flying. This is called Head-Arms Spin in the FUNimation adaptations.
Buto Kaiten: Ranbu (武頭回転乱舞,Butō Kaiten: Ranbu?, literally meaning "Military Head Spin: Wild Dance"): A variant of Buto Kaiten where Chinjao spins faster and has more control over his movements, allowing him to turn more quickly and spin towards his opponent at great speed, occasionally jumping through the air. Luffy stopped the spinning by wrapping his arm around Chinjao's entire body. This is called Head-Arms Spin: Wild Dance in the FUNimation adaptations.
As the 13th head of the Happo Navy, Sai has been trained extensively in the Hasshoken style. Upon successfully bending his grandfather and predecessor's legendary drill-shaped head with his own technique, Chinjao comes to recognize Sai has awakened his true powers and bestows him the true secrets of the Hasshoken technique. His usage of the style is focused on his leg, which has inherited the ultimate technique.
Bujaogen (武脚跟,Bujaogen?, literally meaning "Military Leg Heel"): Sai kicks his target while emitting the Hasshoken shock wave. This allows him to shatter defense while kicking through his target. It was first used against an unnamed gladiator during Block C's match, but was not named until he used it (along with Busoshoku Haki) to block his grandfather's Kiryu Kirikugi, which was able to bend even Chinjao's legendary drill-shaped head. This is called Wujiaogen Heel in the Viz manga and FUNimation adaptations.
Hasshoken Ogi: Kiryu Kirikugi (八衝拳奥義 錐龍錐釘,Hasshō-ken Ōgi: Kiryū Kirikugi?, literally meaning "Eight Impacts Fist Secret Technique: Drill Dragon Drill Nail"): The Hasshoken secret technique bestowed upon his leg upon proving his might against his predecessor. Sai performs cartwheels while imbuing his leg with Busoshoku Haki, and then performs a kick with vibrations emitting from said leg. Chinjao claimed that with this, Sai should be able to break apart the layers of ice in the same way Chinjao did 30 years back. This technique was first used when Chinjao bestowed him the Hasshoken's secret technique upon his leg, defeating Lao G and sending a massive shock wave linear to the kick, as well as creating a fissure along the ground.
The ability to generate and control vibrations is similar to the Gura Gura no Mi, although the Hasshoken are more of concentric waves than the Gura Gura no Mi's apparent bubbles of concentrated seismic energy.
This fighting style has so far only used by members of the Chinjao Family who are also members of the Happo Navy.
Hasshoken can be based on Bajiquan, a Chinese martial art, which emphasizes using ones' feet, knees, hips, body, shoulders, elbows, arms, and head to attack. It translates as Hakkyokuken in Japanese and it means Eight Extremities Fist in both.