  We present deep JWST NIRSpec observations in the sightline of MACS
J1149.5+2223, a massive cluster of galaxies at $z=0.54$. We report the
spectroscopic redshift of 28 sources at $3<z<9.1$, including 9 sources with the
detection of the [OIII]4363 auroral line. Combining these with 16
[OIII]4363-detected sources from publicly available JWST data, our sample
consists of 25 galaxies with robust gas-phase metallicity measurements via the
direct method. We observe a positive correlation between stellar mass and
metallicity, with a $\sim0.5$\,dex offset down below the local relation.
Interestingly, we find a larger than expected scatter of $\sim0.3$\,dex around
the relation, which cannot be explained by redshift evolution among our sample
or other third parameter. The scatter increases at higher redshift, and we
attribute this to the enrichment process having higher stochasticity due to
shallower potential wells, more intense feedback processes, and a higher galaxy
merger rate. Despite reaching to a considerably low-mass regime ($\log
M_*/M_\odot \sim7.3$), our samples have metallicity of $\log$(O/H)$+12>7$, i.e.
comparable to the most metal poor galaxies in the local Universe. The search of
primordial galaxies may be accomplished by extending toward a lower mass and/or
by investigating inhomogeneities at smaller spatial scales. Lastly, we
investigate potential systematics caused by the limitation of JWST's MSA
observations. Caution is warranted when the target exceeds the slit size, as
this situation could allow an overestimation of "global" metallicity,
especially under the presence of strong negative metallicity gradient.
