Incredible.
Basically, it was impossible to know Kanjuro was a traitor because there was 0 evidence he was the traitor. The narrative excuse Oda used was:
- He was born as a theatre actor.
- He lost his emotions.
- He wanted to die.
- He has been a Kurozumi this entire time.
Unless anyone could have known these before hand, it was impossible for anyone to have good reason to claim Kanjuro the traitor or evidence to prove so. More or less, no one had evidence and the best we could do was make guesses. Heck, he could just as well have claimed Raizo was the traitor because there was no evidence and all he'd have to do is say:
- He was born an actor.
- A Kurzomi.
- Wanted to die.
And we'd just have to accept it.
This is in essence a deus ex machina trickery. Creation of a convenient excuse to get a desired purpose without build up or evidence.
While it's a cheap method of tricking the audience (readers), it's still effective because Oda rarely and ever pulls out this kind of devices in his writing. Oda usually hints and leaves trails of evidence, but I guess here, there's none unless I'm not seeing them.
Not a fan of such methodology, but it does add a spin to the story and add more tension and I guess... surprise.
As for Denjiro, it seems he actually did slash Komurosaki. I had wondered how exactly it was possible to fake a death in front of people, but it's only really possible to fake deaths when no one is around
e.g. You go missing or you plant fake evidence in a place for people to find to come to the conclusion you're dead.
Regardless, Oda pulled it off very well.