  Ringdown gravitational waves of compact binary mergers are an important
target to test general relativity. The main components of the ringdown waveform
after merger are black hole quasinormal modes. In general relativity, all
multipolar quasinormal modes of a black hole should give the same values of
black hole parameters. Although the observed binary black hole events so far
are not significant enough to perform the test with ringdown gravitational
waves, it is expected that the test will be achieved in third generation
detectors. The Japanese gravitational wave detector KAGRA, called bKAGRA for
the current configuration, has started observation, and discussions for the
future upgrade plans have also started. In this study, we consider which KAGRA
upgrade plan is the best to detect the subdominant quasinormal modes of black
holes in the aim of testing general relativity. We use a numerical relativity
waveform as injected signals that contains two multipolar modes and analyze
each mode by matched filtering. Our results suggest that the plan FDSQZ, which
improves the sensitivity of KAGRA for broad frequency range, is the most
suitable configuration for black hole spectroscopy.
