Solve the Mystery as Okarin!
When Okarin and his friends made the "PhoneWave (name subject to change)," they had no idea it would have the ability to send e-mails to the past and, as a result, change the present.
Tragedy strikes as an organization behind a global conspiracy seeks to obtain their invention and threaten the fate of humanity!

But even when the outcome changes, their fate ends in disaster time and time again...
Faced with overwhelming despair, which future will Okarin choose?
Change the past to save the future!

[From Spike Chunsoft]