SSpiegel -- so much agreement for your analysis. Especially about the importance of face in the Asian culture, and especially since Doctor is in an Asian sub-culture -- a Korean in Japan. The way he acted with submissiveness to his boss was appropriate -- it does not reflect his level of courage or willingness to stand up for himself. It's a work context, and in an Asian work context, especially Japan and Korea, other things come into play, way more than your own personality or beliefs.
I would also have liked to see Doctor speaking in Korean to his sister. It would have been way more natural. But that would have meant additional Japanese subs. I agree that his acting smoothened out in the second episode, and in the third as well! They're definitely growing into their roles.
About the third episode...