  Neutron star merger remnants are unique sites for exploring neutrino flavor
conversion in dense media. Because of the natural excess of $\bar{\nu}_e$ over
$\nu_e$, the neutrino-neutrino potential can cancel the matter potential,
giving rise to matter-neutrino resonant flavor conversion. Under the assumption
of two (anti)neutrino flavors and spatial homogeneity, we solve the neutrino
quantum kinetic equations to investigate the occurrence of the matter-neutrino
resonance within a multi-angle framework. We find that isotropy is broken
spontaneously, regardless of the mass ordering. Relying on a hydrodynamical
simulation of a binary neutron star merger remnant with a black hole of $3\
M_\odot$ and an accretion torus of $0.3\ M_\odot$, we find that complete flavor
conversion caused by the matter-neutrino resonance is unlikely, although the
matter and neutrino potentials cancel at various locations above the disk.
Importantly, the matter-neutrino resonant flavor conversion crucially depends
on the shape of the neutrino angular distributions. Our findings suggest that
an accurate modeling of the neutrino angular distributions is necessary to
understand flavor conversion physics in merger remnants, its implications on
the disk physics and synthesis of the elements heavier than iron.
