  We elucidate various aspects of the physics of thraxions, ultra-light axions
arising at Klebanov-Strassler multi-throats in the compactification space of
IIB superstring theory. We study the combined stabilization of K\"ahler moduli
and thraxions, showing that under reasonable assumptions, one can solve the
combined problem both in a KKLT and a LVS setup. We find that for non-minimal
multi-throats, the thraxion mass squared is three-times suppressed by the
throat warp factor. However, the minimal case of a double-throat can preserve
the six-times suppression as originally found. We also discuss the backreaction
of a non-vanishing thraxion vacuum expectation value on the geometry, showing
that it induces a breaking of the imaginary self-duality condition for $3$-form
fluxes. This in turn breaks the Calabi-Yau structure to a complex manifold one.
Finally, we extensively search for global models which can accommodate the
presence of multiple thraxions within the database of Complete Intersection
Calabi-Yau orientifolds. We find that each multi-throat system holds a single
thraxion. We further point out difficulties in constructing a full-fledged
global model, due to the generic presence of frozen-conifold singularities in a
Calabi-Yau orientifold. For this reason, we propose a new database
(https://www.desy.de/~westphal/orientifold_webpage/cicy_thraxions.html) of CICY
orientifolds that do not have frozen conifolds but that admit thraxions.

High Energy Physics - Theory