@Monkey:
And with a crewmate generally one shouldn't feel that way.
Yeah, but this really is a unique situation. Aside from Robin, we have never had a character introduced in an arc prior to the arc they are central to and eventually join in. We've also never really had Luffy without his crew for such a long time, or through such traumatizing events. There is also, of course, the whole timeskip to consider. A lot is there to throw off whatever "patterns" we try and fit these eventual crew members in to, and despite all of them Jinbei fits well, I think.
@Devil:
I just want to pipe in and say that, in my mind, the 10th crewmate…
9th crewmate.
@Monkey:
But that IS important. Oda absolutely has to do that and hard. If Jimbei just kind of plays impassive observer to the fall of Fisher Tiger, Arlong's departure, his own events, and Otohime's death….just sort of being there while these things happened and reacting...then I'm going to fall back into "No he will not join".
That he's having the flashback at all is pretty big, even if we knew it was coming; that he is narrating the flashback in direct response to his guilt and their questioning… I'd be very surprised if he was just an impassive observer. Looking over the entire story of One Piece only two flashbacks have been about people who were a part of the crew: Vivi's and Norland's. Excepting Vivi's, each flashback has told the central role's tragic tale. Excepting Norland's, each flashback has been about events that are directly connected to living cast members. Vivi's was just barely longer than a single chapter. With Jinbei's, going into it we know there will be tragedy, and obviously Jinbei is alive, so already it breaks away from existing exceptions. In addition to this, Jinbei's story (presumably) spans well beyond the death of Fisher Tiger, as it will need to lead up to his actions with Arlong, and it is likely it will go even further and connect to Otohime's assassination. Anyway, all of that to say it would be difficult to even make Jinbei an impassive observer given the context, and looking at Oda's track record with flashbacks, I find it even harder to believe that the person narrating his own tale of regret will be so disconnected from his own story.