"Tsukihi" refers to God the Parent (refer to 5.61).
"Shrine" refers to a building where a deity is enshrined and worshiped.
"Shrine of Tsukihi" is the Shrine where God the Parent resides, which refers to none other than Oyasama.
Oyasama's causality was that She had the soul of the mother during God the Parent's creation of human beings. Oyasama was born in this world on April 18, 1798, in accordance with the promise God made at the time of creation. She was kindhearted from childhood and lived an exemplary life as the lady of the respectable Nakayama family until She was forty-one. Then when the promised time came on October 26, 1838, God the Parent took residence in the body of Oyasama and began conveying through Her mouth the teachings to bring about world salvation.
For the next fifty years, Oyasama--as the Shrine of Tsukihi and as the mother of all humanity--taught with parental love single-heartedly devoted to world salvation and demonstrated the Divine Model, a life that all humans ought to emulate.
It is important to note here that Oyasama's life after She became the Shrine of Tsukihi was completely different from Her life as a human being. Although Her outward appearance was the same, Her becoming the Shrine meant that God the Parent took residence in Her body and spoke through Her mouth, leaving no trace of the human mind that existed before. In other words, Oyasama singly acted and spoke according to God the Parent's intention, without any human thinking whatsoever. God the Parent taught this as follows:
These thoughts of Tsukihi are spoken through Her: the mouth is human, the mind is that of Tsukihi.
Listen! I, Tsukihi, am borrowing Her mouth wholly, and I, Tsukihi, am lending My mind wholly.