  We present the results from the Suzaku X-ray Imaging Spectrometer observation
of the mixed-morphology supernova remnant (SNR) HB9 (G160.9+2.6). We discovered
recombining plasma (RP) in the western Suzaku observation region and the
spectra here are well described by a model having collisional ionization
equilibrium (CIE) and RP components. On the other hand, the X-ray spectra from
the eastern Suzaku observation region are best reproduced by the CIE and
non-equilibrium ionization model. We discuss possible scenarios to explain the
origin of the RP emission based on the observational properties and concluded
that the rarefaction scenario is a possible explanation for the existence of
RP. In addition, the gamma-ray emission morphology and spectrum within the
energy range of 0.2$-$300 GeV are investigated using $\sim$10 years of data
from the Fermi Large Area Telescope (LAT). The gamma-ray morphology of HB9 is
best described by the spatial template of radio continuum emission. The
spectrum is well-fit to a log-parabola function and its detection significance
was found to be $\sim$25$\sigma$. Moreover, a new gamma-ray point source
located just outside the south-east region of the SNR's shell was detected with
a significance of $\sim$6$\sigma$. We also investigated the archival HI and CO
data and detected an expanding shell structure in the velocity range of $-10.5$
and $+1.8$ km s$^{-1}$ that is coinciding with a region of gamma-ray
enhancement at the southern rim of the HB9 shell.
