Berryz's ballads are all good. Koishiteru blabla, Semi, Natsu Remember you, etc. This rule doesn't apply for them. :p
The title is called
"Munasawagi Scarlet" (胸騒ぎスカーレット), they said that their radio show.
I don't think it's from their play, since I don't see anyone talk about it, yet.
Oh I should just mention this here. There was a rumour before the release was announced that TAKUI would be doing this single. If you don't knowwho he is (neither do I), just youtube him. He's like a little Tsunku.
This rumour was taken from a Takui thread on some 2ch board.