noun
memorial service for Nichiren
A memorial service for Nichiren held on the 13th day of the 10th month in Nichiren Buddhism. The term is specific to this tradition.
See also: 会式
お会式は毎年十月十三日に行われます。
The memorial service for Nichiren is held on October 13th every year.
会式 without the honorific お can refer more broadly to Buddhist memorial services, but お会式 specifically denotes the Nichiren memorial service.
From お (honorific prefix) + 会式 (Buddhist memorial service). The term is specifically associated with the memorial service for Nichiren.