  By using the ultra-deep \textit{JWST}/MIRI image at 5.6 $\mu m$ in the Hubble
eXtreme Deep Field, we constrain the role of strong H$\alpha$-emitters (HAEs)
during Cosmic Reionization at $z\simeq7-8$. Our sample of HAEs is comprised of
young ($<35\;\rm Myr$) galaxies, except for one single galaxy ($\approx
300\;\rm Myr$), with low stellar masses ($\lesssim 10^{9}\;\rm M_{\odot}$).
These HAEs show a wide range of UV-$\beta$ slopes, with a median value of
$\beta = -2.15\pm0.21$ which broadly correlates with stellar mass. We estimate
the ionizing photon production efficiency ($\xi_{ion,0}$) of these sources
(assuming $f_{esc,LyC} = 0\%$), which yields a median value $\rm
log_{10}(\xi_{ion,0}/(Hz\;erg^{-1})) = 25.50^{+0.10}_{-0.12}$. We show that
$\xi_{ion,0}$ positively correlates with EW$_{0}$(H$\alpha$) and specific star
formation rate (sSFR). Instead $\xi_{ion,0}$ weakly anti-correlates with
stellar mass and $\beta$. Based on the $\beta$ values, we predict $f_{esc,
LyC}=4\%^{+3}_{-2}$, which results in $\rm log_{10}(\xi_{ion}/(Hz\;erg^{-1})) =
25.55^{+0.11}_{-0.13}$. Considering this and related findings from the
literature, we find a mild evolution of $\xi_{ion}$with redshift. Additionally,
our results suggest that these HAEs require only modest escape fractions
($f_{esc, rel}$) of 6$-$15\% to reionize their surrounding intergalactic
medium. By only considering the contribution of these HAEs, we estimated their
total ionizing emissivity ($\dot{N}_{ion}$) as $\dot{N}_{ion} = 10^{50.53 \pm
0.45}; \text{s}^{-1}\text{Mpc}^{-3}$. When comparing their $\dot{N}_{ion}$ with
"non-H$\alpha$ emitter" galaxies across the same redshift range, we find that
that strong, young, and low-mass emitters may have played an important role
during Cosmic Reionization.
