  Subaru Strategic Program with the Hyper-Suprime Cam (HSC-SSP) has proven to
be successful with its extremely-wide area coverage in past years. Taking
advantages of this feature, we report initial results from exploration and
research of expansive over- and under-dense structures at $z=$ 0.3-1 based on
the second Public Data Release where optical 5-band photometric data for $\sim$
eight million sources with $i<23$ mag are available over $\sim360$ square
degrees. We not only confirm known superclusters but also find candidates of
titanic over- and under-dense regions out to $z=1$. The mock data analysis
suggests that the density peaks would involve one or more massive dark matter
haloes ($>10^{14}$ M$_\odot$) of the redshift, and the density troughs tend to
be empty of massive haloes over $>10$ comoving Mpc. Besides, the density peaks
and troughs at $z<0.6$ are in part identified as positive and negative weak
lensing signals respectively, in mean tangential shear profiles, showing a good
agreement with those inferred from the full-sky weak lensing simulation. The
coming extensive spectroscopic surveys will be able to resolve these colossal
structures in three-dimensional space. The number density information over the
entire survey field will be available as grid-point data on the website of the
HSC-SSP data release (https://hsc.mtk.nao.ac.jp/ssp/data-release/).
