What I really like is that it makes language and discussions between characters that much more interesting, as you have to keep track of what he might be understanding or not. It's kind of a low key anxiety watching the scenes, knowing lots is probably going over his head and he's feeling extremely out of place. He just looks strained and bewildered much of the time, as he's trying hard to keep up. And then in key moments it drives home how much of communication is also delivery and body language. It's just so entertaining to have this as a central concept in this story.
Yeah the most recent episode was really interesting with that where we didn't spend much time with his PoV, so it was very hard to get a sense of what exactly he knew and didn't know. They made it clear that he's starting to pick up
some amount of Japanese, but we don't ever get a clear read of how much or how little since Mariko would often be there to translate.
It'll be interesting to see how the finale goes since communication might be a much bigger issue now.
I still didn't get for what Torinaga needs Blackthorne in Osaka. He made clear that he wanted Blackthorne to join Yabushige, and he is using Yabu predicting behavior to execute his plan, but I am failing to see Blackthorne's part in it.
My read was that it just helps sell that Torinaga has fully given up and lost Blackthorne to where Yabushige was able to buy his loyalty. Blackthorne has the reputation of mostly caring for self-preservation and very much wanting Torinaga to fight, so for Torinaga's Hatamoto to abandon him (especially in public fashion where he stormed out of the surrender announcement) it just helps sell the performance.
It's also just pragmatic imo. Blackthorne wouldn't have much to do sitting around the camp, so being able to go with Mariko and protect her and be a tool she can use for the role she had to play would just be strategic. Like how he was able to be an excuse for Ochiba and Mariko to meet.