Re: Sensei? Sempai?
My understanding of "sempai" was that it was usually one-half of the "sempai-kohai" relationship - where the sempai is a senior who took a kohai (junior) under his wing. I don't know if the same relationship traditionally exists for women - it may, and the terms may even be the same, or different - I only observed it in males in Tokyo.
At our dojo in Regina Saskatchewan, we were developing a sempai-kohai system. One of the things we had (we used coloured belts there) was that the more senior students (sempai) handed down their coloured belt to their kohai when the kohai was graded to that colour of belt. We were held responsible for our kohai's etiquette errors and if the kohai's ukemi wasn't up to our sensei's expectations, the kohai didn't take the thrashing, the sempai did...