  In this note, we study the Swampland Distance Conjecture in TCS $G_2$
manifold compactifications of M-theory. In particular, we are interested in
testing a refined version -- the Emergent String Conjecture, in settings with
4d $N=1$ supersymmetry. We find that a weakly coupled, tensionless fundamental
heterotic string does emerge at the infinite distance limit characterized by
shrinking the $K3$-fibre in a TCS $G_2$ manifold. Such a fundamental
tensionless string leads to the parametrically leading infinite tower of
asymptotically massless states, which is in line with the Emergent String
Conjecture. The tensionless string, however, receives quantum corrections. We
check that these quantum corrections do modify the volume of the shrinking
K3-fibre via string duality and hence make the string regain a non-vanishing
tension at the quantum level, leading to a decompactification. Geometrically,
the quantum corrections modify the metric of the classical moduli space and are
expected to obstruct the infinite distance limit. We also comment on another
possible type of infinite distance limit in TCS $G_2$ compactifications, which
might lead to a weakly coupled fundamental type II string theory.
