The Ultra Dimension (神次元, Kami Jigen) makes its first appearance in Hyperdimension Neptunia Victory as an alternate Gamindustri that resembles the Hyper Dimension in 1989. In this dimension, CPUs are not born as goddesses but rather humans and instead require an item known as a CPU Memory to transform. Once they have become a goddess they are then allowed to form their own nations in Gamindustri.
The time in the Ultra Dimension is different compared to the Hyper Dimension; one day in the Hyper Dimension is equal to a year or more in the Ultra Dimension. This time flow is stabilized in the true ending of the game.
The Ultra Dimension is more or less similar to the Hyper Dimension but with some differences. While Planeptune, Lowee and Lastation are on the mainland, and Leanbox is on an island separated from the three, there are also continents to the east and west.
In the western region there is a continent known as the Hello Continent and in the eastern region there lies the PC Continent. On the mainland, directly next to Lowee, there lies Eden which is considerably small in comparison to the other nations.
In the past, there were no CPUs and Gamindustri was a chaotic place with constant skirmishes and death. The people wished for a time where a goddess would come and create a nation, bringing peace to Gamindustri. Eventually, the Rei Ryghts of the Ultra Dimension stumbled upon a CPU Memory and ate it because she was starved and believed it to be food.
It was then that she met Croire and learned that she had become a CPU and could create her own nation. This resulted in the birth of the nation known as Tari. At first, the people were pleased to finally have a goddess they could worship and a nation they could live in. However, Rei's tyrannical nature began to become far too much for the people. Many of her followers began to turn on her which caused her power to weaken.
Infuriated at this, Rei decided to take matters into her own hands and destroy everyone which had lead to her nation tumbling down and her losing all the faith that she had obtained from her people. After reverting to her human form, she began to think about her actions and began to believe that the fault lied within all CPUs and not herself. This event leads her to believe that CPUs should not be allowed to exist.
Years after Tari's fall, Lowee was founded by the CPU White Heart. For a long time, White Heart was the only CPU in all of Gamindustri. However, after Plutia accidentally consumed a CPU Memory which leads her into becoming the goddess known as Iris Heart and forming the nation of Planeptune.
While Planeptune did take some shares from Lowee, White Heart was not concerned with the loss of shares as Plutia was lazy and did not bother to try and increase her shares.
Hyperdimension Neptunia Victory
When Neptune had arrived in the Ultra Dimension Gamindustri, the only two nations were Planeptune and Lowee. Because of the rules of becoming a CPU were different in her world as opposed to the Ultra Dimension, Neptune was completely stripped of her goddess powers and was nothing more than a mere human. This realization made her also seek a CPU Memory along with Noire to regain her power and prevent herself from aging.
Once Noire had finally become a goddess with the aid of the CPU Memory, she founded her own Nation known as Lastation under the divine name Black Heart. Noire's hard working personality put a considerable dent into Lowee and Planeptune's shares. This concerned Blanc, while Plutia was not concerned as much due to being friends with Noire.
Not too long after, the nation of Leanbox was formed by Vert who was known by the divine name Green Heart. Despite a forth nation popping up, Vert's console had many complaints, and as a result, her shares did not go up as much to impact the other nations.
While initially rivals, the actions of the Seven Sages, a group of people who are against CPU rule that is lead by Rei, the four CPUs work together to prevent things from going out of hand. The sages were unable to do anything major to harm the goddesses until they created a CPU for themselves. The Seven Sages attempted to kidnap children to turn them into goddesses but failed to do much. It wasn't until they found out that Peashy was a CPU by eating one of the CPU memories Rei had, so Anonydeath took her from the Basilicom. Yellow Heart founded the nation of Eden, which had a devastating impact on the other nations' shares.
After finding out that Yellow Heart was actually a brainwashed Peashy, the CPUs helped regain her memory. Peashy left Eden and became a CPU of Planeptune.
In the true ending of the game, the Ultra Dimension becomes connected with the Hyper Dimension through a large portal powered by shares. This portal also stabilized the time flow between the two dimensions.