That ghost chick Persona was sent away by Kuma to the same place Zoro was, which was Mihawk's home, so they kinda just got along ther I guess, since she was the one who brought him back to Sabaody.
I can't find a video on youtube of when Luffy gets that scar, but I can say it happens in episode 487.
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Easiest bracket ever, yet we all failed!
Well except SuperNiceDog, of course!