Ah, the cliché, "can't see an opening," line, to describe how amazing of a warrior he is. It's just bullshit. Being that skilled means you can hide your intentions, and if you're good enough to actually see through it, you're good enough to see the openings that are there, but in reality you can see none of that, because that's not how it works. A fine example of "He's good, trust me, bro."
A straight bladed sword isn't that different from a katana. They don't curve that much. A lot of sword techniques were very similar between Japan and Europe, since at the end of it, there are only so many ways to handle a sword that are efficient.
So, is he going to return while Asvald is still alive?
not to say katanas and the like aren't cool just that other historical japanese weapons deserve more love in isekai fantasy
Same is true everywhere. Swords were not nearly as ubiquitous as main weapons as they appear in fiction. They were mostly sidearms.
Concerning the matter of half-bloods, it seems like they only crop up because humans can't keep it in their pants. I see no mention of half-bird, half-fish here, nor did we hear about half-elf, half-dwarf back home.
Add to that that half-races are always called by their non-human part. It's always half-elf and never half-human, regardless of whether it's humans or elves talking.