It is also referred as Jusannichiko (lecture of Buddhist scriptures, composed by congregation of Hokke sect) because it was held before and after 13th day every month, having to do with the day when Nichiren, founder of the sect, died.
同宗の祖である日蓮が没した日にちなんで毎月13日あるいはその前夜に開かれたことから十三日講とも称する。