Sorry for the random bump, but the last couple of diary entries have been interested.
One of them dealt with the PV, showing some specific screenshots and discussing the green-haired girl that was with Akyuu in one of the still images, even going as far as releasing a small bio on her.
Apparently her name is Tomoko Kujino, but beyond that I have no clue. Beyond that, they have posted an exact screenshot of the silhouettes from the PV.
Not much we can work out from this, but all things considered with SB's previous work, here be the culprits.
The entry after that was actually a summary of the entire Omen Trilogy, including the previous two games. Interestingly enough, Devil of Decline is a prequel to Genius of Sappheiros, not a sequel, and it added some more specific plot details concerning the ultimate ends of each of the previous two games (such as Angra and co returning to Makai but coming back occasionally and the Gorgons staying as guardians as promised). Also, the chronology of the trilogy goes as follows:
Devil of Decline ("The Chaos Incident"): Early summer, most likely following the events of Ten Desires
Genius of Sappheiros ("The Blue Gods Incident"): Midsummer of the same year
Lingering Summer Heat ("The Resentment Incident"): Late summer of the same year
Nightmare of Rebellion ("The Doppel Incident"): Winter of the following year
They teased a bit about whether or not this new incident is related to the previous ones or not. Whatever the case, I find it interesting they'd summarize the previous games in relation to this new one.