  We revisit the evidence for CMB birefringence in the context of a rich
Axiverse. Using probability density functions (PDFs) for various axion
parameters, such as the mass and axion decay constant, we construct the PDF for
the cosmic birefringence angle and investigate its properties. By relating the
observed value of the birefringence angle to the mean or standard deviation of
the constructed PDF, we constrain the shape of the input PDFs, providing
insights into the statistical distribution of the Axiverse. We focus on three
different types of axion potentials: cosine, quadratic, and asymptotically
linear axion monodromy. Our analysis showcases the potential of cosmic
birefringence in constraining the distribution of axion parameters and
uncovering possible correlations among them. We additionally offer predictions
for "birefringence tomography," anticipating future measurements of
birefringence from lower multipoles, and show how it can be used to rule out
simpler versions of the Axiverse. Our findings contribute to the ongoing
exploration of the Axiverse and its implications for cosmic birefringence.
