By reading Chapter 20 of Main Story 2 (JP), you can unlock the new song, TWiNKLE CiRCLE, but there seems to be something else in this chapter..?
Hm..? Both of them are also fully voiced, and I know Mashiro was missing a voice before... Very interesting...
Oh, if you didn't know, the left girl's name is ましろ, Mashiro, she's appeared in previous Main Story 2 Chapters. The new girl on the right is 透子, Touko (at least, that's what her name is listed as).