Wow, this feels like a Touhou Tonari speedrun. Yukari and Yuyuko's relationship has always been highly mysterious, exacerbated by the fact that both parties involved are ridiculously secretive and obtuse on their own.
You'd think they'd at least be honest with each other, and maybe they are, but even the most intimate of outsiders can't tell, since they've reached a level of closeness beyond words. But in that case, you also couldn't tell if they were arguing. It's a nightmare for everyone involved, but there's something very self-destructively romantic about it. Unless you're Youmu, in which case, you only get migraines.
Interesting to see yukayuyu in a different perspective, to see Yukari being her whimsical self to mask how much it hurts to be by Yuyuko's side.
Now I feel like reading Percol's and Vizionners Yukayuyu again...