Project Mirai is the 3DS spinoff of the Project Diva series of Vocaloid rhythm games.
Project Mirai DX is the updated re-release of Project Mirai 2, and is being localized and released on May 26th in NA, 28th in JP, 29 in EU, and apparently TBA 2015 for AU.
About the game:
It has a lot of cool extras like a song creator (you get a little keyboard with different instruments, and you can arrange notes on a sheet to make a song with them) and a dance creator (similar, you pick a song and choose dance moves for either each second, or each bar, don't remember).
There's also something fun called "my room" where you can dress up the chibi Nendoroid style Vocaloids in the various costumes from the song PVs and watch them walk around and interact with various furnishings, like using a DJ booth.
You can even dress them up in each other's costumes, and edit the colours of some of the costume details.
You can also feed them different beverages and deserts, like shortcake. It's all really adorable.
The gameplay itself is really customizable.
There's two control schemes you can choose from, button mode and touch mode. In the former you press buttons and the D-pad in time to the notes, and in the latter you tap different coloured drums on the touch screen.
There are three difficulty levels for each song, with each one having an extra colour and more notes over the last, as well as more D-pad notes in button mode.
It starts at two colours for button and one for touch.
Touch mode is generally a bit easier, and also less likely to ruin your buttons -_-
You can also customize what sound is played for each note, as well as note colours, and the coolest part is that you can customize everything individually per song.
You can change the costume used in the PVs too, and change the singer(s) for some songs.
I've played Mirai 2, and it's quite a fun rhythm game, especially if you're in to Vocaloid music.
Personally I'm super hyped to be able to play it in English, so that I'd be able to use things like the song and dance creators properly. Plus there'll be (official!) subs on some of the songs I haven't bothered to look up yet.
Also, I think the PV theater has some sort of NicoNico-esque online comment-sharing-thingie, although I was never able to figure out for certain, and it getting localized might be iffie.
I think they still weren't able to make Gumi playable, which makes me sad :(
I hope you can at least put her costumes on the other characters this time.