  Negative magnetoresistance is rare in non-magnetic materials. Recently, a
negative magnetoresistance has been observed in the quantum limit of
$\beta$-Ag$_2$Se, where only one band of Landau levels is occupied in a strong
magnetic field parallel to the applied current. $\beta$-Ag$_2$Se is a material
that host a Kramers Weyl cone with band degeneracy near the Fermi energy.
Kramers Weyl cones exist at time-reversal invariant momenta in all symmorphic
chiral crystals, and at a subset of these momenta, including the $\Gamma$
point, in non-symmorphic chiral crystals. Here, we present a theory for the
negative magnetoresistance in the quantum limit of Kramers Weyl semimetals. We
show that, although there is a band touching similar to those in Weyl
semimetals, negative magnetoresistance can exist without a chiral anomaly. We
find that it requires screened Coulomb scattering potentials between electrons
and impurities, which is naturally the case in $\beta$-Ag$_2$Se.
