Tomo - Drums (I think most of the forum can agree on this XD) + Backing vox
Haru - Lead guitar(Haru solos?! ) + Lead vox
Mami - Bass + Backing vox
Rina - Rhythm guitar + Backing vox
I think this would be an awesome arrangement. Haru is able to shred some awesome solos, Rina gets to sing more AND BE CLOSER TO THE FANS AT CONCERTS, Mami would look so groovy with her bass lines, and hyperactively-cuteTomo would be pounding away on the drums.YEAH!