Since its operation, the Hyper Suprime-Cam (HSC) mounted on the Subaru telescope has
been discovering a number of distant (z > 6) quasars, owing to its powerful survey
ability.  As quasars are the "beacon" of supermassive black holes (SMBHs), they are
the ideal laboratory to investigate the cosmic evolution of the SMBH mass vs host galaxy
mass relation (so called "co-evolution" relation).

In this seminar, I will summarize our series of ALMA observations toward such HSC
quasars.  We have revealed: massive (>10^10 Msun) host galaxies at that early universe,
wide variety of star formation activity (from starburst to almost quiescent), mergers of
galaxies that may be related to quasar activities, quasar-driven powerful outflow that
terminates star formation, and the early shape of the SMBH-host mass relation.  I will
gauge these points from the perspective of "co-evolution", and also discuss our future
plans including JWST and ALMA observations.