Iroha and her Magical Girl friends decide to open a dialogue with the Uwasa known as Endless Solitude, which is also the name of the realm (essentially a labyrinth) where Futaba Sana currently resides. The Uwasa is being used by Wings of Magius to lure girls in one after the other.
The realm only holds one (hence “solitude”) so when a new girl enters, the other is released. The Uwasa doesn’t want to do this anymore, and wishes to be deleted. Since Iroha was the Uwasa’s contact, she volunteers to leap off the Chuo Radio Tower.
Flash back to a little over a month ago when Futaba Sana first entered the Endless World and met the Uwasa, a former AI that was abandoned as a failure. Sana had become resigned to the fact she didn’t belong in the same world as everyone else, since nor peers acknowledged her existence.
Her “invisibility” was only strengthened when she became a Magical Girl, and made that quality her wish. It was then when Sana heard of the rumor about jumping off the radio tower and was enticed. She was an invisible girl here anyway, so why not try to reside somewhere else…a world just for her?
It was there where Sana met, befriended and named Endless Solitude’s Uwasa “Ai”. She spent her days playing around this fantastical, infinite world, where she didn’t have to worry about seeing or be seen. It was just her and Ai, and that’s where things get tricky for Ai: Sana is content in this world and never wants to return to the real world.
Knowing Sana would never attempt to leave, Ai reached out via radio waves to Iroha, another Magical Girl who’d not only survive the fall, but be able to destroy her, the Uwasa, in order to end the cycle of captured girls. However, she doesn’t tell Sana about any of this.
As such, it’s a huge shock to Sana to finally be face-to-face with a second person in a world that’s supposed to be hers and hers alone. And yet, Ai has already decided that returning to her world is what’s best for Sana, even if it’s painful at first.
Needless to say, Sana isn’t pleased by these events, and asks if this is being done because Ai has come to hate her. Ai responds that the opposite is true: because she loves and cares for Sana so much, this has to happen…and Iroha stands ready to help.
That’s when another magical girl/Wing of Magius (not exactly sure which) appears out of nowhere and is introduced as Alina Gray by Ai, as if that’s someone we’re supposed to know! Alina mixes Japanese with English as she moves to prevent Ai from being destroyed. I was a little confused by this sequence, but I’d guess Alina wants to keep Ai around as her own Doppel.
Ai manages to teleport Alina away temporarily, but they have to act fast to foil her plans, as Alina’s “paint” has already started to affect Ai’s programming. She turns to Sana, not Iroha, to put the proverbial (and later, literal) dagger into her chest, revealing herself as Sana’s Doppel, which explains why they got along so well; they are two sides of the same coin.
Faced with the prospect of Ai being corrupted and stolen from her, Sana does what Ai asks and destroys her after a heartfelt goodbye. Back in the real world, the other girls don’t notice anything happening where they are at the radio tower, but deduce that Endless Solitude’s exit is at the other high point of the city: Kamihama Central Tower, and head that way to await Iroha’s return.
With this, the final character in the promo art is introduced, and it being a bit late, her story feels a bit rushed and shoehorned in with a lot of exposition, while Futaba Sana’s “I’m all alone” storyline has been done to absolute death. At least the Shaft-style visuals keep things relatively interesting during all the backstory.