Hassaikai

Hassaikai is a huge kanabo, the iron war club Kaidou carries as his trademark armament. Forged from solid black metal with a circular cross-section, its heavier upper half is studded with sharp spikes before narrowing toward a smooth, spikeless grip that ends in a suspension ring acting as a pommel. The proportions are built to match Kaidou's own towering size, and he has wielded this very club since joining the Rocks Pirates as an apprentice more than forty years ago.

The club anchors nearly all of Kaidou's close-quarters fighting. Driving it with overwhelming strength and routing Supreme King Haki through the metal, he can maim opponents and hurl them great distances with one swing, gripping it in either one or both hands, the latter for his heaviest blows in Human-Beast Form. It doubles as a shield to bat away incoming attacks. One swing felled Kouzuki Oden two decades back and knocked out a Gear 4 Luffy in the present, smashing through his Armament Haki. Its central technique, Raimei Hakke, is a blinding horizontal charge so fast that even Luffy's future sight could only half-dodge it, and it spawns variants like the fiercer Horai Hakke and the double-strike Daiitoku Raimei Hakke. Other named blows include the descending smash Kosanze Ragnaraku, the ranged shockwave Kongo Kabura, the rapid barrage Gundari Ryuseigun, the air-blade Kaifu, and the team-up Hakai performed beside Big Mom's Napoleon.

Kaidou of the Beasts Pirates is the sole wielder, his son Yamato copying the Raimei Hakke to lesser effect. Per Oda, Hassaikai holds no formal rank, yet would be called a legend if Kaidou ever set it down. The name draws on Buddhism's eight precepts, and many of its techniques are titled after the Five Wisdom Kings. Oda has also sketched the club anthropomorphized as a bulky, top-heavy old man who refuses to go outside.