Technically the instrument Atago has there is a sousaphone, not a tuba, but I'll leave the tuba tag because a euphonium (which RJ has) is really a kind of tuba (it's a tenor tuba, same dynamic range as a tenor trombone; the one people think of as just a tuba is in fact a bass tuba).
Kirishima's John, the cerebral one. Kongou's Paul, the charismatic frontman. Haruna's George, the quiet one with the most interesting musical ideas. And Hiei is Ringo, who's just happy to be there.