  It is easy to reason that gravity might be the effect of a fluid in disguise,
as it will naturally arise in emergent gravity models where gravity is due to
the effect of some fundamental particles, with the latter expected to behave
collectively like a fluid at the macroscopic scale. We call this the
fluid/gravity equivalence. The key difficulty with the fluid/gravity
equivalence is to find the correct metric-fluid relation (the relation between
the emergent metric and the fluid properties) so that the fluid not only has
physically acceptable properties but also obeys the usual hydrodynamic
equations, while at the same time the emergent metric also obeys the Einstein
equations. Faced with the problem, we have previously made a tentative proposal
of the metric-fluid relation, focusing only on obtaining physically acceptable
predictions on the fluid properties. In this paper, however, we find that for
the general gravitational wave spacetime near the null infinity, the underlying
fluid not only has physically acceptable properties, but also satisfies the
expected relativistic hydrodynamic equations in the Minkowski background, thus
providing a concrete example satisfying both of the major requirements expected
for the fluid/gravity equivalence.
