Much has been speculated about the identity of the mysterious prisoner in Wano. And the egregious theorist inside me naturally did his own humble research so here’s my theory:
Let me start by enumerating some of the traits that this prisoner have.
He seems to have high tolerance to poison.He also seems to endure hunger pretty darn well.
To cut the suspense short, I present to you my own candidate on who is the prisoner beside Luffy and Kidd.
Yes, ladies and gentlemen, I think he is Gin from Baratie Arc. Based on their conversation above, it gave us a hint of a possible return by Gin on the main storyline. Luffy already crossed the Grand Line but we have yet to see Gin, not even updates about him was shown. He also fits those two descriptions above. He was introduced as a hungry prisoner who sought food at Baratie.
His poison tolerance was possibly developed after he inhaled Krieg’s MH5 gas. It was hinted that he should be dead after inhaling those gases but we already know how that usually pans out.
*Theory by Anjo