He uses Ittoryu, or One Sword Style, and has apparently mastered it, being able to easily take Nitro on for most of their fight.

Turbulent Maelstrom

Hamiki's most power attack, and what he claims gave him his Beli Small22mil bounty.
Hamiki's Attack

Hamiki using Turbulent Maelstrom

He spins around at a great velocity, then dashes at his opponent, putting all the force he's gathering into a single strike,