I don't think they have. Though Atsuro see's him more of a mentor, I guess? Which works for them, I guess.

[He can't help that another laugh escapes him at that. Yeah, a lot has happened between him and Naoya, but...]

Honestly, when I was growing up? I looked up to him a lot. I was always clinging to him and following him around. Always trying to impress him in some way or another. Not that I didn't annoy him on purpose later, but that's what siblings do. The younger siblings are meant to annoy the older ones.