Since the plan of Kozuki Momonosuke and the Nine Red Bao group along with Luffy’s group was revealed, many theories about finding Kaido’s `insider` have always been of interest to the audience.
1. Evidence from Zou Island
First of all, the traitor was definitely the one who leaked all the information to Orochi.
As for the Minks, there was very little reason for them to betray the Kozuki family.
2. Details and some hints show that Kanjuro is a `countlessly innocent` person.
One Piece chapter 940, when Luffy’s side learns that Yasuie and his allies will cooperate to fight in the upcoming great battle, Kanjuro is there. And right after chapter 941, how miserable is Mr. Yasuie?
Continuing with chapter 955, when Kawamatsu tells the story of Hiyori, Kanjuro is also there.
Many people coming here will think that there is another suspect, Ms. Shinobu, but this character has an alibi.
3. Some other small hints about the hand in Kanjuro
Chapter 920, when everyone knew that there were still many people out there loyal to the Kozuki clan, everyone was happy, only Kanjuro did not show any signs of emotion, could this be a hint from Oda.
And no one knows what Kanjuro did in Dressrosa, only according to Kinemon that he was taken hostage and found in a normal and `comfortable` state, even eating cabbage.
Kanjuro’s devil fruit ability is completely suitable for being a spy for the Orochi faction when he can completely draw pigeons of all kinds to deliver news.
Above are the very strong and well-founded arguments of many viewers about finding the Traitor in the Nine Red Bao that we have compiled.
Reference: [ESOP] Hypotheses, debates, answers about One Piece