  Unveiling the dark sector of the Universe is one of the leading efforts in
theoretical physics. Among the many models proposed, axions and axion-like
particles stand out due to their solid theoretical foundation, capacity to
contribute significantly to both dark matter and dark energy, and potential to
address the small-scale crisis of $\Lambda$CDM. Moreover, these pseudo-scalar
fields couple to the electromagnetic sector through a Chern-Simons
parity-violating term, leading to a rotation of the plane of linearly polarized
waves, namely cosmic birefringence. We explore the impact of the
axion-parameters on anisotropic birefringence and study, for the first time,
its cross-correlation with the spatial distribution of galaxies, focusing on
ultralight axions with masses $10^{-33}\,{\rm eV}\le m_\phi\le10^{-28}\,{\rm
eV}$. Through this novel approach, we investigate the axion-parameter space in
the mass $m_\phi$ and initial misalignment angle $\theta_i$, within the
framework of early dark energy models, and constrain the axion-photon coupling
$g_{\phi\gamma}$ required to achieve unity in the signal-to-noise ratio of the
underlying cross-correlation, computed with the instrument specifications of
Euclid and forthcoming CMB-polarization data. Our findings reveal that for
masses below $10^{-32}\,{\rm eV}$ and initial misalignment angles greater in
absolute value than $\pi/4$, the signal-to-noise ratio not only exceeds unity
but also surpasses that achievable from the auto-correlation of birefringence
alone (up to a factor 7), highlighting the informative potential of this new
probe. Additionally, given the late-time evolution of these low-mass axions,
the signal stems from the epoch of reionization, providing an excellent tool to
single out the birefringence generated during this period.
