  KAGRA is a newly build gravitational-wave observatory, a laser interferometer
with 3 km arm length, located in Kamioka, Gifu, Japan. In this paper in the
series of KAGRA-featured articles, we discuss the science targets of KAGRA
projects, considering not only the baseline KAGRA (current design) but also its
future upgrade candidates (KAGRA+) for the near to middle term (~5 years).
