Re: Sempai-Kohai relationship
FWIW, years ago when I joined my current dojo I remember sensei clapping and everyone sitting down. I stood back to see what they did -- totally random placement. Lined up, but yudansha mixed with mudansha. No order. Just sit. So I sat on one end.
When sensei said "practice" we paired up with whoever bowed to you first. Gokyu or godan, it didn't matter. I loved it.
Nowadays I make a point when I'm taking a class to go find the newer students and sit next to them. So they don't feel quite so nervous when I bow to them when we're supposed to practice.
Yes, I still know who are my sempai. And who are kohai. But it is mostly a irrelevant detail day-to-day.
There are always customs/rituals/etiquette in every context. But sometimes we in the west try so hard to emulate what we think is right we end up taking things to an absurd level.
Lots of good posts in this thread explaining what sempai/dohai/kohai means. "When in Rome..." as the old saying goes is still of course relevant. But I always wonder when I see people who take it to the extremes. Seems too much attention paid to appearances and not enough on the good stuff that's supposed to be inside all that stuff...