Aikido

Aikido (合氣道, aikidō) is a modern martial art known as "the way of unifying life energy". The primary goal in the practice of Aikido is to overcome oneself instead of cultivating violence, and so it offers the user unparalleled power if they are able to master it, which few have ever done.

Of all its styles, the Sonozaki-style Aikido is said to be the most powerful, and one of the most almighty fighting styles in the world. The only other martial art said to be capable of besting it is the dreaded Systema, to which nothing can stand against.

Sonozaki-style Aikido
Of its differences, there's a single one that is the most important: it's approximately 1000% more badass than regular Aikido.

Sonozaki Steven, a man who brought a revolution to combat arts as a whole, developed this style in display of both his unending kindness and unlimited power. It was said Aikido guided both his body and soul, and because of that he never had to fear loss in a fight, bringing death to all those foolish enough to keep challenging him.

Steven himself taught many of its techniques to members of the Sonozaki Family, but only Steven remained the sole Master of the style, only teaching the full extent of its power to the greatest of his disciples, Matou Kariya and Kiryu Kazuma, who were the only true heirs to it.