Headscratchers / Shinrai: Broken Beyond Despair

• What kind of accent is Nobara supposed to have? Additionally, why doesn't her father talk the same way?
• Given that the game takes place in Japan and most of the teenagers at the party don't know each other all that well(most people have at least one close/best friend, but other than that, they're mainly acquaintances), why is Last-Name Basis the exception(Runa towards everyone, Kamen toward Raiko), rather than the norm?