  Nodal-line superconductor NaAlSi with a transition temperature ($T_c$) of 7 K
has attracted considerable attention in recent years, whereas its Ge
counterpart, NaAlGe, does not superconduct down to the lowest temperature
regardless of their similar atomic and electrical structures. To tackle this
enigma, we resort to the growth of NaAlGe single crystal and characterize its
semimetallic ground state. Interestingly, when hole doped by oxidation,
single-crystalline NaAlGe transforms from a semimetal to a superconductor ($T_c
= 2.3 \sim$ 3.5 K) with zero resistivity and a diamagnetic shielding fraction
over 100$\%$, but without a thermodynamic response in heat capacity. Continuous
x-ray diffraction reveals a transient new structure with a larger $c$ axis,
which is suggested to have arisen from the minor loss of Na and to be
responsible for the emergence of the delicate superconductivity. Our findings
resolve the controversies in NaAlSi and NaAlGe, while their similarities and
differences provide an ideal opportunity to investigate a variety of exciting
topological quantum states.
