He is going to be cagey initially about his own situation whenif the subject of demonic possession comes up, because while most people on the train are probably like "Shabranigdu? Is that like, a kind of pasta?" where he comes from most people would freak the fuck out about the idea of Shabranigdu possibly being amongst them.

It won't be impossible to get the story out of him though, if Ryou seems relatively calm and discreet, and at the very least Rezo is going to be Extremely Interested to hear about Ryou's situation.