Shio Sakaki holds the position of master at Ryozanpaku Dojo, bearing the title "100-Dan Street Brawler of Karate" and ranking as the fourth oldest among its instructors. He possesses a tall, heavily muscled frame with tan skin and short eggplant-colored hair, marked by one longer strand falling across his face. A horizontal scar crosses his nose bridge, sustained in his late teens. His typical attire includes an open brown leather jacket worn over a bare chest, blue jeans, and bandages wrapping his forearms; during Kenichi Shirahama’s training sessions, he dons a traditional karate gi. His clothing frequently tears from muscle expansion when enraged.

Sakaki blends intimidation with concealed compassion. He projects arrogance and violence, often appearing intoxicated, yet remains Ryozanpaku’s most "normal" master. Unintentionally terrifying even at rest, he flusters when this is noted. A kind, caring nature wars with his hot temper and inept lying—traits he fails to hide. Quirks include stage fright under public scrutiny, evident when posing as Miu Furinji’s father, and initial difficulty interacting with children due to his aura, though he eventually connects. Among Kenichi’s mentors, he exhibits deepest concern for the disciple’s safety, worrying during fights or isolation. He trains Kenichi rigorously out of care, signaling pride with subtle gestures like rubbing a finger under his nose. This mentorship shifts from initial reluctance to accepting Kenichi as his first disciple, breaking Ryozanpaku’s non-interference rule to protect him. Sakaki habitually gambles, drinks, and bets on Kenichi’s matches. His mood sours in Kenichi’s absence. He embarrasses easily over minor issues, such as Kenichi using "sensei," and shares Apachai Hopachai’s intimidating laugh. Despite a Satsujinken master’s upbringing, he practices Katsujinken—a conviction solidified after his friend Suzuki’s death by Akira Hongo. A running gag positions him as Ryozanpaku’s "closest to evil" master, reflected in Miu misreading his ki as hostile, Kenichi’s early fear, his villainous declaration against Kushinada, and his demonic pursuit of Yami members.

As a fighter, Sakaki ranks among Earth’s supreme karate masters, rivaled solely by Akira Hongo. Originally offense-focused, he adopted defense after Suzuki’s advice to minimize openings. Unrestrained, he overwhelms lethally, requiring ally intervention. His skill impressed Yami’s Silcardo Jenazad, who craves a death match. Sakaki displays acute combat perception, identifying karate styles from stances and adapting tactics mid-battle. Physically, he wields immense strength—lifting cars, flicking people airborne—deceptive speed outpacing vehicles and creating afterimages, and extreme durability surviving high falls unharmed. His Dou-type ki radiates as a natural intimidating aura, potent enough to disintegrate fabric and fell groups with a glare. It matches Hongo’s ki in clashes, causing destruction. He speaks fluent English from FBI work and U.S. residency, alongside Japanese.

Sakaki’s past involves international travel, FBI collaboration for high-risk missions, and a nose scar from battling Hongo. He has an unseen but formidable sister. Jenny claims him as her fiancé due to a drunken vow. He struggles technologically, baffled by devices like mobile phones.

His character arc centers on mentorship. Initially opposing disciples, he grows deeply invested in Kenichi’s growth, secretly lauding his courage and shedding proud tears when Kenichi nearly dies shielding others. He violates dojo rules to aid Kenichi in peril and voices loneliness during his absence. His patience with children evolves, seen while training Honoka and another child, despite early struggles.