User blog comment:Kaido King of the Beasts/Chapter 940: The Eleventh Straw Hat/@comment-27930128-20190419095802/@comment-34962159-20190420062858

It's possible that Caribou (and other characters in this arc) will end up joining the Straw Hat Grand Fleet, instead of becoming a full crew member.

The three characters may have been introduced to explain Hiyori's actions when she was acting as Komurasaki - she was swindling criminals instead of innocent citizens.