So we have Jane Smith and John Doe. They are high school students in Japan. Jane is a first or second-year student and John is a third year student. They've known each other for a year or two, and while they aren't close, close friends, they're past the calling-each-other-by-their last-name stage, but not close enough to call each other just 'Jane' and 'John.'
So, I know that the term for upperclassman is 'sempai (though I think I may have also seen it as 'senpai,' but my handy copy of Trigun #1 says sempai, so any thoughts on that matter...?),' but what would they call each other? Would Jane call John John-sempai? Or just John-san? Or simply Sempai? And what in the world would John call Jane?
Just some basic info on how upperclassmen and underclassmen who are friends would address each other.