Complex sentence: Another place Amakusa Shiro is mentioned is in "Rurouni Kenshin", where his self-proclaimed successor Amakusa Shogo is cast as a character in an anime-only arc of the series.
Split into simpler sentences: Another place Amakusa Shiro is mentioned is in Rurouni Kenshin. His self-proclaimed successor Amakusa Shogo is cast as a character in an anime-only arc of the series.