Immediately you're thrown off because you were expecting the stereotypical highschool movie party but the use of popular music covered in the medieval style of instruments has you intrigued. Imagine you come up to the gate by the vault entrance, it's closed and you hear the faint sound of loud medieval covers of popular songs. In fact, Raihan seems like the kind of guy to answer the door in full cosplay and welcome everyone who wanted to join in on this "party" with the full intent of throwing the most immersive D&D roleplay campaign. While at the same time, Raihan throws "parties." As in he invites the whole school to his house, the castle, for a giant group D&D session. Raihan seems like the kind of guy who, in a highschool setting, he'd be the popular guy who knows everyone by name and talks to everyone and is cool with everyone. He has, on more than one occasion, referred to himself as "the great Raihan." That is the dorkiest thing ever and it's adorable. Raihan acts like he played D&D as a dragonborn character once and decided he wanted to be his OC for the rest of his life cause he thought they were so cool.
The scratching at the air and screaming seems like a thing Raihan thought looked cool and decided it was a thing he was gonna do from now on. Sure he scratches at the air and screams during battle, sure he screams out his commands for his Pokemon team, but that all seems like an act for the audience watching. Piers is the guy who tells you no encores and not to call him when something goes wrong again. Piers is more feral than Raihan in the sense that Piers is the kind of guy who'd probably bite you as a warning. He acts feral but that's really just the persona he displays for everyone to see. When one really thinks about it, Raihan's a dork.