For my post, it's just a small crowd. xD It's not really an arena per se. :P It takes place at the field outside. Based on Swifty's beginning post, I figured anyone could have a different duel depending on their preferences. Either they want just a few spectators or a huge crowd spectating students facing a giant hard-leveled robot.
& Bastian, I'm perfectly sure there are other students than just us, which is why I added an NPC in my post. I'm sure that's allowed lol.