I was watching an AJPW tape with clips from the mid 90s and in every match there are a number of young men all dressed uniformly who stand around the ring. Because I don't know any better, who are they? The ring crew? Dojo students? Security?
They always clean up the streamers that were thrown in during introductions and always checked on both wrestlers after the match.
It's common for all major organizations in Japan. Most of the time, they are either dojo trainees or rookies, and they are "seconds" like boxing and also serve as security. Mid-carders are often included.
You'd see guys such as Onita, Fuchi, Tarzan Goto, Koshinaka, Misawa, Kawada, etc. in earlier AJ stuff.