The official Miku Twitter account has given us looks at three additional songs in Hatsune Miku: Project DIVA Mega Mix. In addition, the blog post gives us a first glimpse at the opening movie of the game.
UPDATE - Gematsu has translated the details..
■ New Songs
“Jigsaw Puzzle” (music and lyrics by Mafumafu)
“Roki” (music and lyrics by Mikito-P)
■ Theme Song “Catch the Wave” Music Video Introduction
The theme song “Catch the Wave,” which is written by kz (livetune) for Hatsune Miku: Project Diva MegaMix, is the Hatsune Miku: Project Diva series’ 10th anniversary commemoration song.
—Module “Catch the Wave” designed by LAM
The theme of the in-game music video is “to be able to connect with anyone, anywhere” and thus features scenes that connect people around the world.
The opening movie features Hatsune Miku and Piapro characters.