  Recently, Kawaguchi and Nakayama (KN) [Phys. Rev. E {\bf 88}, 022147 (2013)]
showed that the hidden entropy production associated with a coarse-graining
procedure obeys the integral fluctuation theorem (IFT) if the original process
does not involve any odd-parity variable that changes its sign under time
reversal. This was interpreted as the evidence that odd-parity variables play
an important role in the derivation of irreversible stochastic dynamics from
time-reversible deterministic dynamics. In this Comment, we show that KN's
approach is inadequate for describing the origin of irreversible stochastic
dynamics, which calls into question whether odd-parity variables are required
for the emergence of macroscopic irreversibility.
