"Onyudo" Wadatsumi (大入道ワダツミ Ōnyūdō Wadatsumi) is a giant tiger blowfish fishman and a member of the Flying Pirates under captain Vander Decken IX.

"Onyudo" (大入道 Ōnyūdō), Wadatsumi's nickname, literally means "large, bald-headed monster" or "giant". "Umibōzu", which is what Usopp incorrectly refers Wadatsumi as, means "sea bonze", a Japanese mythological spirit. Wadatsumi's name itself is derived from "Watatsumi", the name of the Japanese sea god and dragon of Shinto religion.

First Appearance: Chapter 606; Episode 525