Issa Mihotoke, more commonly known by his nickname Fat Buccha or simply Buccha, is a prominent character recognized for his immense physical strength and surprising agility on Air Trecks. Before becoming a founding member of the team Kogarasumaru, Buccha was the leader of a rival gang called the Night Kings (also known as Yaou), which he controlled at Higachu Junior High School. After losing a Parts War against the protagonist Ikki, his team disbanded and he was recruited to join the newly formed Kogarasumaru, transforming from an antagonist into a stalwart ally.

Buccha has a distinctive and deceptive appearance. He is a tall, heavily built young man with tanned skin, a bald head, and three distinctive scars or lines on his forehead, a design homage to the professional wrestler Abdullah the Butcher. He is usually seen wearing headphones and a pink and white striped shirt. While he initially appears to be obese, this physique is misleading; his body composition is only about ten percent fat. His large size is actually caused by an unusually high volume of blood—over ten times that of a normal human—pooling in his midsection. This blood can be consciously redirected, allowing his appearance to shift from rotund to a much slimmer, immensely muscular and toned figure, which also grants him extended reach.

In terms of personality, Buccha exhibits a notable duality that aligns with his physical transformation. In his daily life, he is a friendly, amicable, and somewhat easygoing individual whose primary interests are eating and relaxing. He is also known to be able to dance. However, when a serious battle begins, his demeanor shifts dramatically. He becomes a focused, devastating combatant, driven by a fierce competitive spirit. Initially depicted as a bully who abused his power and collected emblems to prove his worth, his defeat at the hands of Ikki humbled him. After joining Kogarasumaru, he shed his bully-like attitude and became a fiercely loyal friend and teammate.

Buccha's role in the story is that of the team's power fighter, often characterized as a human tank. He serves as the primary close-quarters combat specialist and a physical bulwark for the group. His primary motivation evolves from a desire for personal dominance to a commitment to his team and the goal of conquering the sky. He follows the Rock Road, a path that aligns with his unyielding and heavy-hitting fighting style. Throughout the series, he undergoes significant development, primarily focused on mental discipline. His father, a Buddhist monk, subjects him to rigorous training, including catching boulders thrown from a waterfall, to help calm his mind and sharpen his concentration. This training allows him to better control his battle instincts and unlock more of his latent potential, earning him the moniker "King of Mountains" for his ability to withstand devastating shockwaves.

His key relationships include his rivalry-turned-friendship with Ikki, who serves as his leader and inspiration. He also has a close bond with his teammates, particularly with the more agile riders who rely on his strength. His father plays a significant role as a mentor for his mental and spiritual growth.

Notable abilities are centered on his unique circulatory system and the technique known as Bump Up. By redirecting the massive volume of blood in his gut, he can pump it into his muscles, dramatically increasing his strength, size, and even speed. On offense, he wears studded gloves or brass knuckles to amplify his already crushing blows. He has shown the ability to send blood to his lower body to enter a High Speed Light Tank Mode, sacrificing upper body mass for incredible velocity. Furthermore, the iron and oxygen stored in his hyper-dense blood allow him to withstand extreme pressure and hold his breath for over twenty minutes, enabling him to fight effectively underwater. His ultimate power is the ability to generate powerful vibrations from his body, which he can emit as destructive shockwaves.