Information gatherd so far:
It is an Expansion for Scarlet Weather Rhapsody, but can be played Stand-alone, installing it on SWR will enable characters from SWR to be playable.
It's Deck system has recived an upgrade, featuring at least 20 different System Cards.
New Spellcards and Skillcards will be available for exisiting characters.
New available characters:

Sanae Kotiya, the Shrine Maiden of Morya Shrine. Initially lived in the outside world. Moved to Gensokyo so the gods she worships would gain more faith.

Cirno, a Fairy that lives around the Misty Lake. Not very bright, also known as: "⑨"

Hong Meiling, the gatekeeper of the Scarlet Devil Mansion. Also refered to as "China" due to her apperance.
And a possabillity of a new unlockable character
Each of these characters means a new weather effect based off of each of them
A new story mode has been added, story made by ZUN himself. The primary story involves a large object that appered around the Youkai Mountain, then vanished. This story involves the new characters introduced.
There are also other stories available that involve day-to-day life of the Girls of Gensokyo.