New info from a 4gamer interview:
Source: Gematsu
The game is the next numbered entry in the Neptunia series and depicts three stories set in three separate dimensions. They are:
Zero Dimension Game Neptune Z: Ragnarok of The Abyss Goddess
Hyperdimension Neptunia G: Gold Vanguard Gamindustri Existence of Change
Heart Dimension Game Neptune H: Trilogy Final Into the Legend
Initially, Compile Heart thought of releasing each story as a separate titles, and thus created different logos for each.
In the Zero Dimension, a new character named Uzume Tennohboshi, the The Abyss Goddess, will be at the storys focus. (In fact, shell be a key part of each dimensions story.) Neptune and her younger sister Nepgear find themselves blown into the world of the Zero Dimension, where they come across Uzume and an adult-like Neptune. This adult-looking Neptune is said to be a different person from the regular Neptune.
The battle system of Neptunia VII will be completely new. Its said to be close to the traditional system, however, the structure of combos have changed. Character positioning will also be of high importance and play to your advantage in enclosing the enemy.
As previously detailed, each goddess will also have a new Next Form.
Source: Gematsu