Chapter has been out for a long time (to an anomalous degree) so I’m guessing the content’s been talked over several times already. Anyway…
1. Kurourmaru and his clan
So, Kuro was more or less deliberately sent on a suicide mission against Evangeline. His body is ‘accursed’, though whether that refers to his deathlessness as well as/or something else is up to debate. Setsuna was considered ‘taboo’ just for being born white, so again, another possible parallel.
(On another note: Yes, I’m sticking with ‘he’. The ‘Story So Far’ explicitly calls him a ‘boy’, something that did not happen with Shinobu. So unless Akamatsu retcons it… it’s a man, baby.)
As for why those guys were wearing masks… well, who knows, really. They sort of look like theatre masks and some brief Googling told me that there IS a kind of vaguely bird-shaped mask used in traditional dances and variously referred to as ‘bird-helm’ or ‘crow-head’. But that’s looking waaaaaay too deeply into something Akamatsu probably just put in to avoid having to come up with faces for background characters nobody care about.
Finally, Kuro calls the guy ‘Nii-sama’. Again, it’s hard to say if he’s really an older brother or not.
2. Yukihime’s retort
When Touta panics and calls Yuki ‘Grandma’, she responds by calling him ジャリ or 砂利 jari – literally ‘pebble(s)’ and a term I’ve never seen used this way before. This is apparently a stage jargon (and insult), used to refer to the kids in the audience. It’s saying that, looking down from the stage, the kids are so tiny they look like pebbles.
…Nice to see the jibes getting more sophisticated while still carrying the same general meaning. Poor Touta.
3. Kuroumaru’s Shinmei
So… Zanmaken Ni-No-Tachi. That was a bit unexpected. As I remember, Ni-No-Tachi techniques are supposed to be taught only to those related to the founding family of Shinmei (ie. Aoyama). Is Kuro’s clan Aoyama, after all?
As has been noted elsewhere, ‘Ni-No-Tachi’ is now 弐乃太刀 instead of 弐の太刀 from Love Hina and Negima (the ‘No’ is now more archaic). I doubt it actually means anything, though. Actually, I wouldn’t be surprised if it was a typo.
By the way, it doesn’t actually say ‘Achievement Unlocked’ – that would be 実績解除 in Japanese.* Still, that’s a very funny way to put it!
* What do you know, you do learn stuff watching NND game commentaries!