Asano Rain
Anna embodies the Blast sound faaaar better than Mika-chin, but that's no surprise, as Mika-chin's deep, mellow voice is more suited for jazz pieces.
I was watching the music videos for both Olivia as Reira and Anna as Nana (or at least that's the feel the PVs were playing at) and I must say that Olivia makes a MUCH better Reira than Anna does Nana.
I think they're both wonderful for Nana, so I'm good. I don't think either of them overpower one another.
And Olivia is totally Reira. >>; I like Olivia better than Yuna Ito. I still like Yuna, though. ^^'