The term "Service performers" refers to those who are assigned to perform the Salvation Service. God the Parent expresses an urgent desire to gather Service performers throughout the Ofudesaki, a desire that was consistent from the period when it was written to the day when Oyasama withdrew from physical life. Though indispensable to the realization of the Service, it was a difficult task to assemble these Service performers. Since Oyasama was always discerning people's minds to seek those who were suitable to be Service performers, this task implied more than merely having the required number of people.
A total of 75 persons are needed as Service performers and this number has been traditionally broken down as:
"Kagura" -- 10 persons
"Narimono" -- 9 persons
"Teodori" -- 36 persons
"Gakunin" -- 20 persons
The phrase "ten for the Kagura" (Ofudesaki X:39) refers to the dancers who perform the Service around the Kanrodai based on the truth of human creation. These ten dancers each represent and express in their hand movements one of the ten aspects of God the Parent's complete providence that was present during human creation. In the Ofudesaki we read,
When God has accepted the sincerity in the minds of the ten performers of the Service,
These ten dancers are therefore "Service performers" in the narrowest and most important sense of the term. Not only must each of these Service performers be a person who measures up to God's expectations, but it is also important that they melt into the mind of God the Parent and become one, not unlike how the summoned instruments did during human creation. Oyasama had specifically named persons to take the ten dancer positions. However, She had said that even they could have God's providence in their bodies stopped if they used their minds in a manner that was against God's intention or led their lives with a mind unsuitable for the role they were assigned and that they might even pass away for rebirth. In fact, there were some predecessors who passed away for this reason.
I am confident that you, the reader, more or less know what the "Teodori" (Dance with Hand Movements) and "Narimono" (musical instruments) assignments imply. It is not entirely clear at present, however, what "Gakunin" refers to. This role was also called "Fudetori Gakunin" in the past, which literally means "Gakunin who take up a brush." There are variant traditional interpretations of who the Gakunin are, which include, "musicians who play gagaku music," "persons who are in charge of clerical work," or "people who write manuscripts of the Koki (Divine Record)." I wonder if Gakunin might be considered to be those who are involved with the preparation and the planning for the Service rather than persons who are directly involved in its performance. It may also be possible that Gakunin are persons who study the significance of the Service in depth and widely convey their results to others.
From the standpoint of Tenrikyo history, it does not seem that there was ever a time when these "Service performers" assembled completely. There was a case where Oyasama designated someone who was to be born 30 years later as a Service performer. There was another case where someone else often took the place of a person Oyasama had designated a specific position. Of course, such substitutions could not have been freely made at anyone's whim; only those who were specifically allowed by Oyasama could perform the Service. In a wider sense, it appears that such people were also referred to as "Service performers." The second Shinbashira wrote in Hitokoto-hanashi, Vol. III that, "It can be speculated that the reference to 75 persons and so on includes those who are assigned as substitutes."
Later, other people such as the heads of fellowships were also allowed to participate in the Service. After the establishment of Tenrikyo Church Headquarters in 1888, the Salvation Service came to be performed by Honbu-in (senior staff members of Church Headquarters) and their wives who were named by the Shinbashira on top of those who were personally named as Service performers by Oyasama. Further, those who perform the service at the monthly services of local churches are called "tsutome hoshi-nin" in Japanese to make a clear distinction from the Tsutome ninju who perform the Service at Jiba.