  We study the axion portal between the visible and the dark sector, where the
Dark Matter is charged under a simple abelian extension of the Standard Model.
In general, such models are anomalous and are rendered gauge invariant by a
St\"ukelberg axion through Wess-Zumino/Green-Schwarz mechanism. This axion
mixes with other Goldstone bosons in the model to give a physical axi-Higgs
which becomes massive upon breaking the anomalous gauge group. Such axi-Higgs
fields charged under the anomalous symmetry act as mediators for the Dark
Matter annihilation to Standard Model particles and can lead to an efficient
freeze-out mechanism. Here, we show that the St{\"u}kelberg axion and the
resultant axi-Higgs, with its appropriate shift symmetry cancels the quantum
anomalies and also generate the observed relic density for the Dark Matter.
Moreover, we show that the relevant parameter space in our model, where photon
production dominates, is safe from FermiLAT, Cherenkov Telescope Array, and
H.E.S.S. indirect detection experiments.
