While this dungeon is called Ontario Corridor on the map and library of the game, inside of it, the text calls the dungeon "Oratorio Corridor", which is likely its intended name. The reason stems from the fact Oratorio's definition has a more divine meaning as opposed to Ontario.
The following items can be found in the dungeon. Items in the treasure chest can only be obtained once. Numbers are marked on the map to denote those treasure chests.
The CPU rescue mission makes to the dungeon. Older Neptune announces that the CPUs are further ahead. Uzume prepares to meet her fake. Uni prepares to fake the Dark CPU. Rom is scared of the Dark CPU but Ram comforts her. Uzume and Nepgear assure the twins of victory thanks to the Sharing Field ability Uzume possesses.
The mission finally makes it to the inner part of the dungeon to find each of the CPUs trapped inside the Dark CPUs. Uni notes that the Dark CPUs are bigger than she imagined. K-Sha wonders how are they going to free the CPUs. B-Sha wants to use an anti-surface missile. K-Sha is worried about Noire getting hurt. Older Neptune tells her that freeing them by breaking out is the only choice but normal attacks don't work on a Dark CPU.
Kurome Ankokuboshi and Croire arrives. Kurome notes that if she had known older Neptune would have lead them here, she would have killed her earlier. Uzume demands Kurome release the CPUs, B-Sha wants her to tell them why was the Gold Third toyed with and K-Sha just wants to beat her up. Kurome says the purpose of messing with the Gold Third was entertainment because if they fell into delusion, then the world would be chaotic.
B-Sha gets mad and Kurome continues saying that it is time to kill the mission. Uzume asks her how she intends to do that as she has Share Energy. Kurome instead asks Uzume to become one with her as they were originally one person. Uzume gets confused so Kurome decides to return all her memories to Uzume. Uzume struggles to cope with the new memories, so older Neptune and Umio try to help her up.
Kurome says it will take time to process everything so she decides to explain everything. Firstly, CPUs are essentially born from people's wishes. However, for Uzume, her people grew to hate her, plotted her assassination and ended up sealing her. Eventually they forgot about her. Uzume vowed revenge and just like that, her source of power shifted from Share Energy to Negative Energy generated by negative emotions. Using her delusion power coupled with negative emotions of her people, Uzume deleted all trace of herself from her people.
In turn, the people needed a new CPU, Uranus. Nepgear pieces it together, but Kurome announces that she is a CPU of Planeptune, Uzume Tennouboshi and demands they all kneel to her, increasing the gravity of the place forcing the mission to kneel. Kurome then explains that both the Zero Dimension and Heart Dimension are born from her dream of herself destroying Gamindustri, with the Zero Dimension serving only as an entrance to the Heart Dimension.
Uni says that is not possible but Kurome reminds her that her overall power to turn dreams into reality. This is why Planeptune hated her. Kurome tells the mission that she wanted to break out of the seal, but she could not. However, if her dream created dimensions, she break out of their dimensional boundaries instead of the seal. As she began to attempt this method, a part of Uzume split off from her and tried to stop the Dark CPUs trying to break the boundaries.
But that was good for her, as once Uzume battled the Dark CPU and started to gain Share Energy, she did as well. With the Share Energy, Kurome can observe the Hyper Dimension and appear as a hologram but that was enough. Kurome decided to send Arfoire out to gain even more Share Energy. Kurome then came up with the idea to fuse the dimensions instead breaking out of the boundaries or seal. Nepgear, Umio and Uzume are in shock to learn that their adventures in the Zero Dimension only helped Kurome out.
Kurome says that the Gold Third are also to thank. The Golden Summits, that were created give a rare signal in multidimensional space allowing for ease of finding the Hyper Dimension. Their existence was thanks to the CPU Shift Period lowering the faith in the goddess, good enough for her to write the CPUs out of existence. Gamindustri, however needed protectors and created the Golden Summits. C-Sha concludes that both the Gold Third and AffimaX were just playing into Kurome's hand. S-Sha calls Kurome scum.
Kurome continues, saying the fused dimensions will allow her to physically materialize the Dark CPUs. Kurome notes that with her Negative Energy, Uzume's Share Energy, Croire's power that came from another CPU, she can rule Gamindustri forever. She asks Uzume to become one with her again. Uzume refuses and says that if she was a predecessor, she would watch over the current CPUs not do what she has done.
Kurome says it is a shame and will kill her along with the rest of the mission. Uzume says that she is outnumbered. Kurome creates clones of Arfoire and explains that this is her dream, creating things from her memory is easy. She admits that this gave her quite a bit of trouble in the past but serves as a perfect pawn. Nepgear does not care and the candidates transform ready to fight to rescue their sisters.
Kurome tells them not to get too excited as the CPUs just fell into delusion and she allows them to awaken. Neptune is happy to be revived. Noire complains about being confined in the Dark CPU. Vert agrees but notes she feels refreshed. Blanc says she feels the same way. Nepgear is happy to see her sister and gets close to her.
Neptune notices Nepgear and says that she has to kill her. Noire scolds her saying that she is too direct and Neptune should not shock her sister like this. Neptune apologizes and says it would be a shame as she needs to torture Nepgear first. Noire transforms and wonders how she will hurt Uni as she can barely contain her desire to kill her. Blanc meets Rom and Ram and says she wants to kill them. The twins ask why and she replies she hates them then transforms. Vert goes up to IF and Compa and notes that the other CPUs are lucky. She must be content with hurting everyone else, she wonders who should she start with, Neptune's friends or the Gold Third and transforms.
Neptune gets next to her sister and transforms to start strangling her. Nepgear asks why to which Neptune replies she hates her and how she can order Neptune around all the time. Neptune tightens her grip as Nepgear struggles but hesistates as Nepgear makes sounds of agony. Older Neptune intercepts forcing Neptune to let go. The candidates pull back and transform back. Older Neptune wants to escape but Nepgear notes that the CPUs are somewhere in there and she won't let it end like this. She tells older Neptune that her sister did hesistate.
The candidates agree with Nepgear and so does Uzume. IF says if Neptune is being dumb then she will knock some sense into her. Compa says IF never goes easy on Neptune. C-Sha says that she must bring her partner back to the right path. K-Sha says that Noire in front of her is not her friend. She will bring her back. B-Sha says a true hero must make sure everyone walks the right path. S-Sha is in agreement. C-Sha is surprised that S-Sha is taking interest in something. S-Sha says E-Sha can't stand Vert like this and she, herself needs no reason to help her friends. The rescue mission begins their battle to return the CPUs to their senses.
After the battle, Uzume wonders why the CPUs aren't back yet. They should not be wanting to hurt their sisters or anything else they love. Neptune regains her senses and apologizes to her sister for all the horrible things she has done and says she was not herself. Nepgear forgives and Kurome is in shock that they were able to drag the CPUs out of the whirlpool of delusion. She forces more Negative Energy to the CPUs.
The CPUs try their best to resist but are in pain. Kurome tells Uzume that she cannot win. Neptune pleads for Uzume's help. Uzume tells the CPUs they must be able to save themselves or else they can't be CPUs. Nevertheless, she admits they are a hassle and if they need help, she asks everyone to pray that to her that the CPUs can return to their senses. Kurome asks her if she is trying to create a Share Crystal and Uzume says that she is. Kurome says it is impossible but Uzume tells her not underestimate her illusion power.
Uzume with the faith of the everyone creates the crystal and transforms the CPUs to their Next Form. Kurome wonders what are those forms? Croire can't believe that they can neutralize all the Negative Energy. Uzume tells her they did not neutralize it but got rid of all of it.
Neptune thanks her but Kurome unleashes Dark Green at the party. Uzume activates her Sharing Field with the Share Crystal. The party destroy Dark Green but find Kurome smiling. Kurome says that she will win and Noire wonders if she is bluffing. Kurome asks them to check the dimensional co-ordinates. Nepgear checks and notices the dimension much closer to the Hyper Dimension but she says it has only been a short time.
Kurome explains it is because they are in the Heart Dimension, she can bring the Heart Dimension closer to the Hyper Dimension with no resistance. She notes that the dimension are close enough for her to materialize, at least for a short time. Croire creates a portal as the two begin to leave to the Hyper Dimension. Blanc asks her if she is running to which Kurome apologizes and leaves a bunch of fake clones of the CPUs for them to fight. She says she created them to influence their dreams but does not need them anymore. The party can dispose of them in however they wish. The two leaves.
Older Neptune is angry that Croire would leave her. Neptune tells the Nepgear, the candidates and Gold Third to follow Kurome as the CPUs will deal with the fakes. They assure her that their real sisters can beat any number of fakes. The candidates and Gold Third take their leave after Uzume hands them a Share Crystal in case Kurome has anymore Dark CPUs. IF and Compa stay behind to help the CPUs. They state that the CPUs need help since they got captured so easily. Neptune thanks IF, Compa then Uzume. Neptune and Uzume begin to catch up but older Neptune interrupts the two and says they must deal with the fakes.
The fakes have a parody of the CPU's personality, which causes the CPUs to transform back. The two Neptunes wonder if it is some debuff cause by their weird dialogue and movement. Compa asks if IF is going to scold Neptune but IF says that scolding two Neptunes is a waste of calories. Compa wonders if she can make a diet drink out of that. Umio says diets are important but are they ready to fight the fakes. Neptune says she is ready to Umiotaro. They prepare for battle but Umio interrupts her to remind her that his name is Umio. Neptune says oh.
The girls manage to defeat the fakes and Neptune notes that fakes are never a match for the real. Uzume feels sad hearing that and Noire nudges Neptune. Neptune quickly apologizes to Uzume and Uzume forgives her and understands. Croire returns to congratulate the CPUs and group for defeating some many fakes. Older Neptune is surprised to see Croire again. IF asks her what is Croire planning. Croire responds with a question and asks them what are they planning to do after knowing everything.
Noire says they plan to defeat Kurome. Croire reminds them that if they do then the Heart Dimension and Zero Dimension disappear getting rid of Uzume, Umio and all of Zero Dimension's inhabitants. Older Neptune is not happy with the two choices and Croire asks her if she was paying attention. Their choices boil down to letting Kurome do as she pleases which will screw over the Hyper Dimension or stopping her with the consequences that Croire previous talked about.
Older Neptune says Croire is cruel and they cannot choose. Neptune remarks that this must be the part where a third option shows up in a few seconds. Older Neptune agrees and says that the option will likely lead to their happy ending. Croire wonders if the two Neptunes only have games in their head. Well she says they better choose soon as the dimensions are getting closer together.
Umio wonders why must the world being so cruel to Uzume. Croire says it is just Uzume's punishment as she nearly destroyed the Hyper Dimension. Umio wants to know more so Croire reminds him of the strange reports that Nepgear found in the Zero Dimension. Since they were slow on the uptake, Croire decided to repair the data but they never figured it out that the perpetrator was Uzume herself.
Uzume runs away after hearing this. Croire says that Uzume just ran away. IF asks Neptune what they are going to do. Neptune says they must pursue her as someone needs to help her cope with her new memories and leaves.