Extract from Ven. Nyanatiloka's Bio says
In 1920, after being denied re-entry into British ruled Sri Lanka, Nyanatiloka taught at Japanese universities for five years, including at Taisho University where he was assisted by the legendary eccentric Ekai Kawaguchi, and at Komazawa University where he taught with President Yamagami Sōgen (山上曹源), who had also studied Pali in Sri Lanka. He also met with Japanese Theravada monks. He lived through the 1923 Great Kantō earthquake, which destroyed Tokyo, but was surprised to see universities reopen just two months later.
To what extent is Theravāda followed in Japan? To what extent is it taught or studied there? Has Japan produced any Theravada Scholars or Meditation Masters? Which books have they written?