Kawashima: During the W7 arc, after they parted with Merry, I was assigned to One Piece from the chapter where Garp shows up.
That chapter happened to be ranked number 1 in the weekly poll with a massive margin over other manga, and that’s when I realized how awesome this series was.
Oonishi: I started from the chapter where Kid, Law, and other Supernova Rookies showed up. But they weren’t originally planned.
Watanabe: What!? Really!?
Oonishi: It was already decided that the crew will be separated at SA, but we figured that may not be enough to spice things up.
That’s when Mr Oda said “Would it be more interesting if bunch of new characters showed up?”
Then 3 hours after that, he not only finished the designs of all of them, but had the fixed name (“name” is manga term for rough draft of the chapter) with all of them already drawn in.
I don’t think they are assistants, sounds more like editors.
It’ll be cleared up when Q-san posts more I guess.