Ed OConnor wrote:
Somewhat... rank helps define the sempai - kohai relationship(s).
Actually Ed, that's not true. Rank has absolutely nothing to do with a sempai - kohai relationship, except maybe here in the west where it has a misconstrued understanding.
You don't become a sempai when you reach a specific rank, or have been studying for a specific period of time. The sempai kohai relationship is different between individuals, you are sempai in your dojo to anyone (regardless of rank) that joins your dojo after you. You are kohai to anyone (regardless of rank) to anyone that joined your dojo before you.
There are various posts here and on Aikido Journal, one in particular by Peter Goldsbury that outlines the relationship very well. Unfortunately I can't find a link to it right now