Complex sentence: The origin of Renbukai is Shūdōkan-a school name called Renbukai-ryu (錬武会流) had been used in the past, but the school name had no basis of origin.
Split into simpler sentences: The origin of Renbukai is Shūdōkan-a school name called Renbukai-ryu (錬武会流). It had been used in the past, but the school name had no basis of origin.