As he explained it, one day his body suddenly understood sand, and sand him, and he and the sand absorbed each other. Things like this happen to humans sometimes. When people fully accept the land they live in they become one with that land. There are not enough examples for it to have a name, but Mr. Soundman and I call it 'Bound'.
SPOILER WARNING: Part JORGE JOESTAR Spoiler details may follow.
A Bound (バウンド Baundo also written as 結びつき Ties) is a Stand-like ability that allows a person to fully blend into an element or environment, or become the environment itself. This ability is featured in the light novel JORGE JOESTAR along with Wounds.
The information below derives from a source not written by Araki. As such, it may or may not be considered canonW.
A Bound works similarly like a Stand, but only developed by very little people. The users must succumb to the land they live in, as if they are becoming one with it. Bounds are based on the land the user originates from. The only current known users in the light novel are Soundman and Kars.
Pucci names this ability a Bound, because it is 'bound' to its user. Instead of adapting to their environment, Bound users 'become' their land.[1] Because Soundman lives in the desert with his Native American tribe, his body is now currently entirely made out of sand because of his Bound, Dune. Not much is known about Bounds, there is only one in the novel.
Bounds can also have range limits, like Dune; it can morph into anything with its sand, but will become ordinary sand once it gets too far away from Soundman.
