  Accuracy in the topology and statistics of a simulated Epoch of Reionization
(EoR) are vital to draw connections between observations and physical
processes. While full radiative transfer models produce the most accurate
reionization models, they are highly computationally expensive, and are
infeasible for the largest cosmological simulations. Instead, large simulations
often include EoR models that are pre-computed via the initial density field,
or post-processed where feedback effects are ignored. We introduce Astrid-ES, a
resimulation of the Astrid epoch of reionisation $20 > z > 5.5$ which includes
an on-the-fly excursion-set reionization algorithm. Astrid-ES produces more
accurate reionization histories without significantly impacting the
computational time. This model directly utilises the star particles produced in
the simulation to calculate the EoR history and includes a UV background which
heats the gas particles after their reionization. We contrast the reionization
topology and statistics in Astrid-ES with the previously employed parametric
reionisation model, finding that in Astrid-ES, ionised regions are more
correlated with galaxies, and the 21cm power-spectrum shows an increase in
large scale power. We calculate the relation between the size of HII regions
and the UV luminosity of the brightest galaxy within them. Prior to the overlap
phase, we find a power-law fit of $\mathrm{log} (R) = -0.314 M_\mathrm{UV} -
2.550 \mathrm{log}(1+z) + 7.408$ with a standard deviation $\sigma_R < 0.15
\mathrm{dex}$ across all mass bins. We also examine the properties of halos
throughout reionization, finding that while the properties of halos in the
simulation are correlated with the redshift of reionisation, they are not
greatly affected by reionisation itself.
