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* First appearance: Battle 7
* Type: Dou
* Type: Katsujin Ken
* Martial Arts: Karate

Sakaki is a 29-year-old extremely powerful, self-proclaimed 100-dan karate master. He claimed not to take disciples at first, but gradually grew to like Kenichi and is always eager to train him. He has a soft side which he tries to hide behind his tough guy attitude, and is usually the one worrying about Kenichi the most despite acting like he does not care. He is also a terrible liar and often fails to hide his concern for Kenichi. He likes to gamble and can usually be seen drinking alcohol. He is also "fluent" in English after brawling all over the world. He is the fiance of Jennifer Grey(even though Sakaki was drunk and Jennifer was a child at the time he proposed). He is an old friend of Christopher Eclair, a Yami member. Sakaki, Christopher and Mycroft (Possibly a reference to Mycroft Holmes, Sherlock Holmes's older brother) used to team up to fight against the mafia and help the FBI. He refused to kill or use old people or children as hostage. Christopher, tired of Sakaki's methods, tries to ambush him, but Sakaki buries him alive in a desert (when Kenichi learns this, he imagines them being tied up in a hole while Sakaki uses a bulldozer, claiming that the two aren't even good manure). The majority of the underground fighters are scared of Ryōzanpaku and Sakaki in particular. There is little known about his past or why or how he became a martial artist especially of his status. Though his master was said to be a master of "Sei", which means that Sakaki's master was a very logical person at heart though to get him to his level, he must have undergone through unimaginablly hellish training.

One notable trait of Sakaki is that his laugh is threatening, which Kenichi uses when he imitated him in the fight against Ryuuto, Sakaki was unaware that his laugh sounded like that and is actually angered by the fact especially when Apachai makes fun of him.