Tansei-4 was a test satellite to verify the performance of Mu-3S rocket and to test out tecnhologies for future satellites.
The Mu, also known as M, was a series of Japanese solid-fuelled carrier rockets, which were launched from Uchinoura between 1966 and 2006. Originally developed by Japan's Institute of Space and Astronautical Science, Mu rockets were later operated by Japan Aerospace Exploration Agency following ISAS becoming part of it.