  FASER$\nu$ is a newly proposed experiment which will take data in run III of
the LHC during 2021-2023. It will be located in front of the FASER detector,
480~m away from the ATLAS interaction point in the forward direction. Its main
goal is to detect neutrinos of all flavors produced at the interaction point
with superb precision in reconstructing charged tracks. This capability makes
FASER$\nu$ an ideal setup for uncovering the pattern and properties of a light
dark sector. We demonstrate this capability for a well-motivated class of
models with a dark matter candidate of mass around a few GeV. Dark matter
annihilates to a pair of intermediate neutral particles that subsequently decay
into the standard model charged fermions. We show how FASER$\nu$ can shed light
on the structure of the dark sector by unravelling the decay chain within such
models.
