Complex sentence: Although commonly believed to be a fictional character, Ichimura was a real member of the Shinsengumi who joined in 1867 with his older brother Ichimura Tatsunosuke and was the attendant of Vice Commander Hijikata Toshizo.
Split into simpler sentences: Although commonly believed to be a fictional character, Ichimura was a real member of the Shinsengumi. In 1867, he joined the Shinsengumi with his older brother Ichimura Tatsunosuke and was the attendant of Vice Commander Hijikata Toshizo.