I always see Nayuta is mentioned as the "third wheel" between them. But, but I disagree with that 🤔
Unlike Kanata, he perceives situations much better and is the one who always ends up giving his brother own space (betraying) to talk with others.

I like the idea/hc that Nayuta actually intentionally stays with them at some point, just to annoy Kanata. Or even testing both.
Something like: If Suzaku stops bothering Kanata, maybe he let you stay the night next time. (😂)

I think Nayuta has this teasing nature, when is combined with Allen's simple-minded and Kanata's bad temper. It's actually a lot of fun to watch.
In fact, I have a slightly stuck idea of what a talk between Nayuta and Allen would be like. (but i still working with that 😩)