According to Japanese Copyright Law (June 1, 2018 grant) the copyright on this work has expired and is as such public domain. According to articles 51, 52, 53 and 57 of the copyright laws of Japan, under the jurisdiction of the Government of Japan works enter the public domain 50 years after the death of the creator (there being multiple creators, the creator who dies last) or 50 years after publication for anonymous or pseudonymous authors or for works whose copyright holder is an organization.
