  We show that a rotating axion field that makes a transition from a
matter-like equation of state to a kination-like equation of state around the
epoch of recombination can significantly ameliorate the Hubble tension, i.e.,
the discrepancy between the determinations of the present-day expansion rate
$H_0$ from observations of the cosmic microwave background on one hand and Type
Ia supernovae on the other. We consider a specific, UV-complete model of such a
rotating axion and find that it can relax the Hubble tension without
exacerbating tensions in determinations of other cosmological parameters, in
particular the amplitude of matter fluctuations $S_8$. We subsequently
demonstrate how this rotating axion model can also generate the baryon
asymmetry of our universe, by introducing a coupling of the axion field to
right-handed neutrinos. This baryogenesis model predicts heavy neutral leptons
that are most naturally within reach of future lepton colliders, but in
finely-tuned regions of parameter space may also be accessible at the
high-luminosity LHC and the beam dump experiment SHiP.
