Harimau, also known as Harimao, is a character introduced as one of Yabuki Joe's opponents in the second season of the anime. He is a young man who was born and raised deep in the jungles of Malaysia as a member of a remote tribe. From a very young age, he demonstrated extraordinary physical prowess, and by his early teens, he was already able to defeat any animal in the jungle. By the age of sixteen, he had become the strongest member of his entire tribe. His life changed when an English reporter came to document his tribe and, recognizing his raw talent, decided to teach him how to box. The reporter became his manager, and Harimau quickly proved to have a stunning natural aptitude for the sport, winning match after match by knockout in the city.

In terms of personality, Harimau is best described as a feral child. He cannot speak any language other than his own native tribal tongue, so in Japan he communicates only through unintelligible grunts, which contributes to his inhuman and wild demeanor. He is deeply unfamiliar with modern society and technology; the bright flashes of cameras at public events can disorient and agitate him, making him aggressive. His behavior is primal and impulsive. He has a tendency to fight dirty when frustrated in the ring, using unorthodox tactics such as biting and headbutting his opponent. Despite this bestial nature, he does display a sense of pride in his fighting abilities, often smirking or chuckling before unleashing one of his secret attacks. The only simple thing known to pacify him and make him act more normally is feeding him chocolate bars. His lack of conformity to civilized norms is so extreme that he even hospitalized his own manager after a disagreement, demonstrating that he cannot be easily controlled or tamed.

Harimau's primary role in the story is to serve as a challenger for Joe Yabuki. He is brought to Japan and to the Tange Gym by Yoko, who confirms him as an opponent for Joe. Harimau develops an immediate and intense fixation on Joe, wanting to fight him desperately. Every time he sees Joe, whether inside the gym or outside the ring, he tries to attack him, at one point even stealing his boxing gloves. The fighting style he brings to this rivalry is his most notable ability. His technique is completely unorthodox, blending raw street-fighting instincts and jungle-bred agility with formal boxing. This combination of pure strength, animalistic agility, and rule-breaking aggression makes him a uniquely difficult and dangerous opponent to face in the ring.