Shark Brick Fist, or Samegawara Seiken in Japanese, is one of the strong techniques included in the Fish-Man Karate arsenal in the anime and manga series One Piece. Literally, "Shark Tile True Punch" is just a very strong straight punch that can launch people backward with its power. It is most famously wielded by Jinbe, a whale shark fish-man and the helmsman of the Straw Hat Pirates, who is known for his mastery of Fish-Man Karate.
In using Shark Brick Fist, Jinbe focuses his strength into just one gargantuan punch. While physically powerful, this technique is part of Fish-Man Karate, the art to which a person's ability to control water at molecular levels is recognized. It is actually the manipulation of water around the punch that comes in contact with the opponent and creates a shock wave that can inflict damage without having to actually make contact.
Shark Brick Fist has been demonstrated on a number of very famous battles throughout the One Piece series. Most notably, it was during the Fishman Island Arc that Jinbe, while fighting Luffy, used the technique not only to show the power of Fish-Man Karate but also his own strength as an emerging Straw Hat Pirate ally.
The anime's visual representation of the Shark Brick Fist is therefore quite spectacular. Chances are, when Jinbe finally attacks with the technique, his fist will often be seen with a blue aura, which is basically to show the manipulation of water a Fish-Man Karate attack has. The impact it makes can be huge, with a great shockwave shooting at the very instance, underlining the destructive power of the technique.
Shark Brick Fist remains a non-self-standing technique rather than an underpinning foundation on which every member of Fish-Man Karate later modifies in great ways. For instance, Jinbe had an improved version known as "Demon Brick Fist," which he used during the Wano Country Arc. This upgraded technique packs even more power and pays off for Jinbe's continued growth and mastery of Fish-Man Karate.
The fact that this technique is named, again reflects on the aquatic theme prominent in Fish-Man Karate. Not only does "shark" refer to Jinbe's lineage as a whale shark, but it also shows that the animal bears some connotations regarding fierceness and power. The term "brick fist" also implies the solidity and weight of impact one might expect from a strike to be equivalent in force to that of a brick wall.
In the diverse martial arts of One Piece, Shark Brick Fist represents the epitome of the unique advantages Fish-Man Karate has to offer. Most other fighting styles in the series are based on Devil Fruit powers or Haki, but the strength behind Fish-Man Karate is derived from an innate connection to the sea and the ability of its practitioners to manipulate water. This makes techniques such as Shark Brick Fist efficient in marine environments, where fish-men can put their natural abilities into full play.
Shark Brick Fist, along with other Fish-Man Karate techniques, is so famous that it has moved outside the manga and anime into other forms of One Piece media. For instance, it becomes a part of the trading card game for kids by being announced on a card named "Arabesque Brick Fist," where the effect would let you return a character card to its owner's hand—a simulation of the potent impact the techniques of Fish-Man Karate bring in the game.
It should be noted, however, that Shark Brick Fist, for all its force, stems from the user: the situation and immense combat skills. In this regard, Jinbe's mastery of the technique at his arm speaks volumes about years of training with a general understanding of the Fish-Man Karate principles upon which it is developed. This expressly emphasizes that actual importance is given both skills and experience in maximizing abilities of this sort within the One Piece world.