Swordsmanship
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 
22mil bounty.
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,