Under Night In-Birth is getting two new characters -- Chaos(not the Melty/Tsukihime one), and Nanase.
https://twitter.com/narita_ton/status/337829380229320704/photo/1
http://img560.imageshack.us/img560/8460/40568008.png
Chaos is Gordeau's cool-headed partner and is seen in Gordeau's arcade mode story a few times as an information provider. He summons?/controls? a giant lizard with the book, and looks to be a puppet-style character.
Nanase is a sword-user who supposedly manipulates wind.
There is implication that they're working to get a PS3 version of the game out(they are clearly showing off the game on PS3 in the below recording), but it's not confirmed.
EDIT:
http://www.ustream.tv/recorded/33260777
You can see Chaos being selected/played starting at 17:58 and 33:12.