Conducting polymer, Haldane gap, quantum tunneling in single-molecule magnets, photoinduced phase transition, quasicrystal, quantum spin liquid. I am running through various hot topics in condensed matter physics and trying to reveal their underlying theoretical mechanism. Such hot topics year by year are worth exploring for me, yes indeed, but I am playing another “soul music” in my hands for the last decade—a modified spin-wave theory. A spin wave is a spontaneous symmetry breaking emerging in numerous natural phenomena and has its history of more than 100 years. The conventional spin-wave theory is beautiful but fragile in that it is hardly applicable to low-dimensional and/or frustrated magnets. I made a major breakthrough in this theory and have been writing a monograph about a modified spin-wave theory of my own.