He kind of is, by refusing to show any gratitude to the guy sheltering his sister (and now him), keeping her safe, helping her integrate into the modern world, and so on. All because he's a huge siscon. I know the author is now trying to spin it into "No you see, he's only a gigantic asshole to Kanji because he wants to make his easier for his sister to return back home", but I won't be gaslit by this type of obvious attempt to course-correct an immensely unpopular character.