Phantasmagoria of Dim.Dream/Story
This page details the events in the story of Phantasmagoria of Dim.Dream.
Prior to the events of the main scenario, Yumemi Okazaki and Chiyuri Kitashirakawa complete a time/space-traveling ship called the Probability Space Hypervessel and use it to travel to Gensokyo, so that Yumemi can complete her theory to disprove the Unified Theory in the outside world or some variation of it.
Bored once again, Reimu Hakurei, idly wondering when something was going to happen, wanders out to the garden of the Hakurei Shrine, only to find huge ruins have suddenly appeared next to the shrine grounds. Mima reappears, having once again escaped from her seal at the end of Story of Eastern Wonderland, along with Marisa Kirisame, and explains the situation.
The ruins are currently accepting "visitors", and on a pamphlet that had been passed out, it seems that the people in charge of the ruins would present a gift to any visitors. Reimu sees a small notice on the ruins saying that only one person would be allowed inside. In order to decide who it will be, the three are joined by Ellen, Kotohime, Kana Anaberal, and Rikako Asakura in a big battle.
Whoever gets into the ruins first faces Chiyuri Kitashirakawa, and soon meets Yumemi as well. The story unfolds as the dialogue progresses. In order to prove her theory of the existence of magic, Yumemi essentially wants to knock out the player, take them back to the real world, and perform all sorts of experiements on her. Obviously, this goes contrary to what the player wanted to get out of this. Yumemi does, however, promise to grant the player a wish(if it's within her power) should she be defeated in combat, as Chiyuri had originally passed out the pamphlets with false information on them.
Chiyuri's Story and Yumemi's Story
During Chiyuri's story and Yumemi's story, specifically in the final two stages, they must fight themselves. No real explanation is given for this, just some odd dialogue written by ZUN. Though with Chiyuri, apparently the playable one is the Gensokyo version. It's implied that after stage 9 everything is "back to normal".
After the events of the main story, it is implied that Chiyuri and Yumemi take the Probability Space Hypervessel back to the real world. Depending on which character the player used, a different wish will be granted.
Yumemi laments her being born in the real world, and thus being unable to use magic. Angered, she is about to take out something she calls a "four-dimensional positron bomb", apparently capable of destroying the entire world, but is stopped by Chiyuri, who smacks her in the head with a folding chair. She was "just kidding" about the bomb anyway.
Reimu Hakurei's Ending
Reimu wishes to be able to clean the shrine up very quickly. In response to this Yumemi gives Reimu their house-keeping android. The game quickly references Multi, a character from ToHeart, with her face censored out. The house-keeping robot is named Ruukoto; Reimu takes her back to the shrine, and soon realizes that Ruukoto is actually pretty bad at cleaning. Ruukoto is never referenced again in the series.
Mima wishes for Yumemi to stop the moon; that way, it will be night forever, perfect for a ghost like her. Yumemi agrees to place the moon in geosynchronous orbit, and is on her way. Under the eternal moon, Mima decides to go tease Reimu, like usual.
Marisa Kirisame's Ending
Yumemi and Chiyuri initially assume that Marisa wants to make one of them her slave, but instead she wishes for a weapon from the real world. She obtains a small ICBM with a cute face to ride around on named Mimi-chan. Neither her nor Reimu seem to know how to use it, though.
Ellen wishes to open a store called "Fluffy Ellen's Magic Shop". Yumemi and Chiyuri construct it on the Hakurei Shrine grounds. Ellen is happy enough, but Reimu is distraught.
After insisting that she is the police of Gensokyo, Kotohime simply tries to get the two to leave. However, since it's come this far, she ends up just wishing for Reimu herself. It turns out that she just wanted an excuse to lock someone suspicious up in a jail cell, since she says that not many suspicious people are even around these days.
Kana Anaberal's Ending
Kana, being a poltergeist, has been attached to a certain mansion for quite some time. The people there aren't really scared of her anymore, so she wishes that she could move - to the Hakurei Shrine. Afterwards, she proceeds to annoy Reimu when she's trying to sleep.
Rikako Asakura's Ending
Rikako wishes that she had the knowledge of science from the outside world - she mentions it's about five centuries more advanced then Gensokyo's technology. Yumemi agrees to give her a science book of some sort, thinking she wouldn't ever be able to understand what was being explained in it. Quite the contrary, Rikako uses the information to become a famous scientist in Gensokyo. (Maybe)
Chiyuri Kitashirakawa's Ending
Both the Chiyuri from the real world and the Chiyuri from Gensokyo return to the real world with Yumemi to mess with her.
Yumemi Okazaki's Ending
Having collected quite a bit of data about magic in Gensokyo, Yumemi presents her findings to the Academy. However, she's pretty much laughed out of there and expelled.
After eventually getting kicked out of the Academy, Yumemi and Chiyuri return to Gensokyo. Their current whereabouts are unknown, and the two are never seen again in the series.