@Izaya_Onisai To answer your questions (again):
1. Japan is kinda intolerant to those that are different and those that stand out; anyone that really stands up for themselves is more or less immediately branded a delinquent. Hell, defending yourself without a genuine fear that you're going to be maimed or killed is heavily frowned upon in Japan to the point it may as well be illegal, so doing anything other than ignoring it and walking away is just asking for more trouble than it's worth.
2. Do they know that he was forcefully returned? I'm re-reading this series because I didn't realize it had been updated recently and Elka only says that he disappeared, not that he was sent back where he came from? Also, as was previously stated, if you were born and raised in a country where you also lived and had a stable career, would you
really throw it all away in protest? Even in the modern day, that's a pretty stupid move, more so in medieval times where easy transportation was virtually nonexistent and outsiders were suspicious as hell, let alone in a world where multiple sentient species not only exist, but are mildly hostile towards one another. That'd be like an English noble getting pissed at the king for deporting his buddy and moving to France.
3. Because while they're opportunistic as hell and were dicks to one person, they seem to be running a pretty successful nation. Would anyone with even a modicum of a conscience murder a sovereign and fuck over tens (or hundreds) of thousands of people just to satisfy a petty grudge?