As one of the Numbers, Nangi's size seems to be large even by giant standards; in one instance he was shown to utterly dwarf the likes of Jack, who himself is over eight meters tall.
Nangi greatly resembles depictions of oni in traditional Japanese art. He is broadly built and bears a wide mouth full of sharp teeth, including a particularly big pair of upper canines. The Number has round eyes, a wide nose, and short, curly hair of light color, with a matching beard. On his lower body he dons an enormous animal pelt, light-colored with dark stripes, seemingly formed into a makeshift hakama.
On the day of the Fire Festival, the Ninja-Pirate-Mink-Samurai Alliance invaded Onigashima to attack the Beasts Pirates. Nangi accompanied Jack and a large platoon of Beasts Pirates to the roof of the Skull Dome, where they joined Kaido in confronting the Mink Tribe forces when they had transformed into their Sulong forms. After a fierce battle, Nangi was later defeated by the minks.
His name contains the kanji "nana" (七,"nana"? meaning "seven"), and the kanji for "oni" (鬼,"oni"?).