  We study the quasi-hydrodynamics of a system with a softly broken $U(1)$
global symmetry using effective field theory (EFT) and holographic methods. In
the gravity side, we consider a holographic Proca model in the limit of small
bulk mass, which is responsible for a controllable explicit breaking of the
$U(1)$ global symmetry in the boundary field theory. We perform a holographic
Schwinger-Keldysh analysis, which allows us to derive the form of the boundary
effective action in presence of dissipation. We compare our results with the
previously proposed EFT and hydrodynamic theories, and we confirm their
validity by computing the low-energy quasi-normal modes spectrum analytically
and numerically. Additionally, we derive the broken holographic Ward identity
for the $U(1)$ current, and discuss the recently proposed novel transport
coefficients for systems with explicitly broken symmetries. The setup
considered is expected to serve as a toy model for more realistic situations
where quasi-hydrodynamics is at work, such as axial charge relaxation in QCD,
spin relaxation in relativistic systems, electric field relaxation in
magneto-hydrodynamics, or momentum relaxation in condensed matter systems.
