Senpai and Kohai in Japan

I write a lot about the Japanese concepts of senpai, an upperclassman in a school or a senior in an organization, and kohai, the opposite, and how important these concepts are for understanding the country. Foreigners in Japan unconsciously pick up on the senior/junior system, too, and try to help newly arrived visitors get their "gaijin legs" as quickly as possible, just as they were helped by others when they got here. Back when I was an English teacher, a friend of mine and I took a newly-arrived teacher at our school out for drinks so we could get to know him. I suddenly realized the situation we were in, and said to my friend (in Japanese, so the new teacher wouldn't understand), "You and I are the senpai here. We have to pay for these drinks." He nodded, aware of the social obligation of our situation, and the two of us picked up the tab over the protests of the new guy. The role of a senpai is a complex one: you get extra respect, but you must act as a mentor and help those under you.

What was your first senpai anime? I'd have to go with the classic Orange Road.