  Exoplanets in their infancy are ideal targets to probe the formation and
evolution history of planetary systems, including the planet migration and
atmospheric evolution and dissipation. In this paper, we present spectroscopic
observations and analyses of two planetary transits of K2-33b, which is known
to be one of the youngest transiting planets (age $\approx 8-11$ Myr) around a
pre-main-sequence M-type star. Analysing K2-33's near-infrared spectra obtained
by the IRD instrument on Subaru, we investigate the spin-orbit angle and
transit-induced excess absorption for K2-33b. We attempt both classical
modelling of the Rossiter-McLaughlin (RM) effect and Doppler-shadow analyses
for the measurements of the projected stellar obliquity, finding a low angle of
$\lambda=-6_{-58}^{+61}$ deg (for RM analysis) and $\lambda=-10_{-24}^{+22}$
deg (for Doppler-shadow analysis). In the modelling of the RM effect, we allow
the planet-to-star radius ratio to float freely to take into account the
possible smaller radius in the near infrared, but the constraint we obtain
($R_p/R_s=0.037_{-0.017}^{+0.013}$) is inconclusive due to the low
radial-velocity precision. Comparison spectra of K2-33 of the 1083 nm triplet
of metastable ortho-He I obtained in and out of the 2021 transit reveal excess
absorption that could be due to an escaping He-rich atmosphere. Under certain
conditions on planet mass and stellar XUV emission, the implied escape rate is
sufficient to remove an Earth-mass H/He in $\sim$1 Gyr, transforming this
object from a Neptune to a super-Earth.
