Wait, so...everybody is a sempai? That doesn't seem right. How does that work?
Edit: Wait, nevermind, I misread and thought Mayuyu called Mariri sempai as well. IGNORE ME!!!!
It's because Mariri is the only 1st year student in the debate club (and Nononon the only 3rd year).
Yeah, that was obvious enough. I was only confused because I misread the greeting at the beginning and though everybody had been called sempai by everybody.