Sega is adding a Nico Nico Video style comment feature to Hatsune Miku and Future Stars Project Mirai on 3DS. In the game's PV Theater viewer mode, you can write comments which will be splashed across the screen like the comments seen in videos at Nico Nico.
There's a group aspect to the comment writing. You can share your comments with others via Street Pass. Before you know it, your PVs could be covered with comments.
Joining this first look at the comment feature, Famitsu.com has screens of the game's AR mode, where Miku will dance around in the location of your choosing, and the latest songs, on the rocks, Shinkai Shojo (Deep Sea Girl) and Haro Hawayu (I'm not sure but I think this supposed to be like Hello, How Are You). Check out the screens below.