Ryuusei No Bifrost
This is the opening theme. It's actually quite catchy the more I listen to it. The download link below will also contain a no-vocal clip as well. It's very upbeat and fits the anime style that this game delivers.
The Gushing Broken Pipe
This song plays when you fight Black Heart. In some way it resembles a bit of her personally where she's kind of quirky at times, but can be serious too.
The Ruins of Ancient Planeptune
I like this melo-music a bit. Too bad there's no battle theme for it since I would like to have that as well. I like to note that the soundtrack link has a typo on this song where it's spelled Anclent instead of Ancient. Just thought I let you know on that.
"Haaaah ha ha ha!" Oh wait, I usually do 3 samples right? Every time I hear the opening of this song, I can't get that melodramatic laughter out of my head. Damn R4, I mean Arfoire!
Hyperdimension Neptunia OST + Ryuusei no Bifrost