  We present extensive optical/ultraviolet observations and modelling analysis
for the nearby SN 1987A-like peculiar Type II supernova (SN) 2018hna. Both
photometry and spectroscopy covered phases extending to $>$500 days after the
explosion, making it one of the best-observed SN II of this subtype. SN 2018hna
is obviously bluer than SN 1987A during the photospheric phase, suggesting
higher photospheric temperature, which may account for weaker BaII
$\mathrm{\lambda}$6142 lines in its spectra. Analysis of early-time temperature
evolution suggests a radius of $\sim$45 $\mathrm{R_{\odot}}$ for the progenitor
of SN 2018hna, consistent with a blue supergiant (BSG). By fitting the
bolometric light curve with hydrodynamical models, we find that SN 2018hna has
an ejecta mass of $\sim$(13.7--17.7) $\mathrm{M_{\odot}}$, a kinetic energy of
$\sim$ (1.0--1.2) $\times 10^{51}$ erg, and a $^{56}$Ni mass of about 0.05
$\mathrm{M_{\odot}}$. Moreover, based on standard stellar evolution and the
oxygen mass (0.44--0.73 $\mathrm{M_{\odot}}$) deduced from nebular [OI] lines,
the progenitor of SN 2018hna is expected to have an initial main-sequence mass
$<$16 $\mathrm{M_{\odot}}$. In principle, such a relatively low-mass star
cannot end as a BSG just before core-collapse, except some unique mechanisms
are involved, such as rapid rotation, restricted semiconvection, etc. On the
other hand, binary scenario may be more favourable, like in the case of SN
1987A. While the much lower oxygen mass inferred for SN~2018hna may imply that
its progenitor system also had much lower initial masses than that of SN 1987A.
