Complex sentence: From January to September 1921, he lived in Tokyo working as a street proselytizer for the Kokuchūkai, a Buddhist-nationalist organization that had initially turned down his service, but continues to claim him as a member.
Split into simpler sentences: From January to September 1921, he lived in Tokyo working as a street proselytizer for the Kokuchūkai, who had initially turned down his services. The Kokuchūkai, a Buddhist-nationalist organization, continues to claim Kenji as a member.