  We report the H, C, and N isotopic compositions of microscale (0.2 to
2$\mu$m) organic matter in samples of asteroid Ryugu and the Orgueil CI
carbonaceous chondrite. Three regolith particles of asteroid Ryugu, returned by
the Hayabusa2 spacecraft, and several fragments of Orgueil were analyzed by
NanoSIMS isotopic imaging. The isotopic distributions of the Ryugu samples from
two different collection spots are closely similar to each other and to the
Orgueil samples, strengthening the proposed Ryugu-CI chondrite connection. Most
individual sub-$\mu$m organic grains have isotopic compositions within error of
bulk values, but 2-8% of them are outliers exhibiting large isotopic
enrichments or depletions in D, $^{15}$N, and/or $^{13}$C. The H, C and N
isotopic compositions of the outliers are not correlated with each other: while
some C-rich grains are both D- and $^{15}$N-enriched, many are enriched or
depleted in one or the other system. This most likely points to a diversity in
isotopic fractionation pathways and thus diversity in the local formation
environments for the individual outlier grains. The observation of a relatively
small population of isotopic outlier grains can be explained either by escape
from nebular and/or parent body homogenization of carbonaceous precursor
material or addition of later isotopic outlier grains. The strong chemical
similarity of isotopically typical and isotopically outlying grains, as
reflected by synchrotron x-ray absorption spectra, suggests a genetic
connection and thus favors the former, homogenization scenario. However, the
fact that even the least altered meteorites show the same pattern of a small
population of outliers on top of a larger population of homogenized grains
indicates that some or most of the homogenization occurred prior to accretion
of the macromolecular organic grains into asteroidal parent bodies.
