just gonna dump my eosd theories that i know are wrong-ish
I always never thought Sakuya was lunarian because I'm sure someone would notice she wasn't human, like Yukari or Reimu.
I've also had a theory that Remilia had ran away from her parents because child abuse and Flandre followed her without really knowing what was wrong, despite her being beaten herself.
While running away from the sdm mansion they grew up in, they arrived in Japan. With no where to go and no human blood they both almost starved to death. Luckily they found a human village.
Because they were both starving they both basically went on a killing spree for almost a month.
There was also only a few sightings of them, but because of how messy Flandre's kills were they were always seen covered in blood, which coined the name scarlet devils.
Having had their fill the killings were stopped, or at least Remilia stopped, Flandre found it enjoyable and kept going. Remilia was afraid that killing too much of them would attract someone powerful, so she tried to stop her, but failed.
This led to them having a fight which Remi won.
With Flandre knocked out she decided to carry her around and look for a place to live. Remilia actually finds the sdm mansion in Japan. It seems her parents actually tried to follow her but Remilia finds both of her parents dead in the mansion, they seemed to have both died of starvation.
Relimia hides the bodies from Flan before she woke up.
She decides to make up a story on how she found a mansion that looks exactly like their home mansion to Flan when she woke up.
Flan believes this and they live there for a while, but it didn't take long for Flan to go back to the killing spree. She loved the 'Scarlet Devil' label and wanted to keep it going.
Again Remilia tried to stop her, but Flandre continued to defy her until Remilia's fear actually came true.
A vampire assassin had arrived in the village. He came equipped with a big arsenal of anti-vampire knives and specialized in fire magic.
The assassin was able to chase Flandre out of the village. He had also followed her to the mansion to see where they live, this also coined the name scarlet devil mansion.
During all that, Remi had gone out to find a different village to prey on to see if she could direct Flandre's violence in a different direction, but instead she ran into Patchouli.
Patchouli was a magician who lived off the money she earned exorcising demons, but she had run into one too powerful for her. Patchouli did eventually get the demon on it's last legs, so the demon had decided that if it was going to die it will make Patchouli suffer and began laying a curse on her as it died.
The curse would Patchouli a crippling anemia that would eventually kill her in less than a week, Remi had came in at this time and killed the demon mid-curse. In doing so, Patchouli didn't receive a fatal anemia, but one she would have to deal with for the rest of her life.
Of course Patchouli wanted to repay her, but had no way to. Remilia told her she could stay at the sdm mansion until she figured something out. Patchouli agreed with her, but she told Remilia she had some business to take care of first. So Remilia left Patchy and returned to the mansion, only to find Flandre badly hurt.
At this point Remilia got really worried and had considered locking the both of them in the mansion until the assassin left, but Flandre was pissed. How dare someone defy her? So she went back to face the assassin again as soon as she healed up.
Remilia hadn't noticed she disappeared until Flandre started coming back.
When she returned Flandre told Remilia how she was able to kill the assassin's wife. This only made things worse.
The mext day the human village had decided that they had enough and all that were able to fight had geared up to fight the scarlet devils. That night without even notifying the assassin, an army of villagers headed for the scarlet devil mansion. Since the assassin found out where they were they all knew where to go.
Remilia was trying to make sure Flandre staying inside the mansion when the villagers broke down the door to go inside. The sheer number of humans coming after them scared Remilia, but excited Flandre. Despite that, they both ran away to split up the huge group.
Eventually they were both cornered in different places in the mansion. They were given no choice, but to fight practically the entire village.
Back at the village, the assassin only just noticed what was happening and rushed to the mansion, hoping to save much of the villager's lives. The fight at the mansion actually turned into a one-sided carnage. The humans proved no match for Remilia and Flandre and were reducing to pools of blood all over the mansion, the entire mansion basically became a legitimate blood bath. By the time the assassin got there Flandre had already finished off her group.
Driven mad by the amount of blood she felt no fear of the assassin and immediately attacked, but this is when the assassin started to show off his own ability, yes, he could stop time (you migt see where this is going). Although he himself couldn't move while he stopped time, he could use his ability to give him the ability to react much faster than realisticly possible and it gave him time to think about his next move.
Remilia eventually finished off her group and found the assassin and Flandre squaring off at the entrance in the mansion.
At first she tried to stop Flandre, but seeing that she stop at nothing to keep the fight going, so she helped Flandre instead.
The fight was very equal, all three of them had suffered major injuries. The assassin wasn't ready to give up, he had to avenge his wife. He was able to turn the tables and temporarily disable Remilia by breaking both of her arms, but Flandre was still fighting strong, almost as if she had no injuries at all. She started to show off her cloning ability, which threw the assassin off, but also made her too overconfident.
She ended up stepping on a spell circle the assassin had made. She tried to get out in time, but her wings were still in the way went it off. A pillar flames shot up from the spell circle, burning all the flesh on Flandre's wings and back away, the bone was reduced to a blackened state.
Before Flandre even had time to react the assassin had thrown many knives into her until Remilia threw herself at him. Her arms were still broken, but she still fought with her teeth. The assassin didn't have much strength left to fend her off, so he decided to attempt holding back Remilia with words. He tried to make her feel bad for murdering practically the entire village, his family, his wife, he lost almost everything except for his 8 month whom he haven't even named. (yes that's Sakuya). Of course Remilia didn't hold back on killing him, she drank his blood until he stopped moving.
Once he did Remilia immediately went to Flandre's aid, she used the ground to forcefully pop one of her arms back in place and sat Flandre up at the wall of the mansion. Remilia carefully removed the assassin's knives from Flandre's body to make sure they don't slowly kill her, but Flandre was already almost dead from loss of blood. The assassin, was able to get up again despite everything and shuffled to Remilia and Flandre to use his last bit of strength on stabbing Remilia, but just as he was about to, Flandre crushed his eye (which marks the first time she does this). Remilia turns around just in time to see the assassin blow up in front of her.
At this time Patchouli had returned to the mansion to see it literally oozing blood and the sisters both severly injured. Patchy had Koakuma with her, who was a demon she had exorcized a while back and decided to form a contract with her to keep her protected now that she had anemia. Koakuma basically has the rights to Patchouli's life.
Anyway, Patchouli helps Flandre and Remilia using whatever healing magic she knew.
Remilia begged Patchy to do something about Flandre's wings, it would be the debt she wanted to pay.
Patchouli couldn't heal the wings back, so she decided to make artificial ones using her own magic, thus the weird tree branch with crystal ornaments wings were born. Despite how they looked they would let Flandre fly around as if she had normal wings, but if Patchouli herself loses enough magic power or dies, Flandre wouldn't be able to fly.
Anyway, Flandre had become unconscious because of the fight, so Koakuma carried her in the mansion (which is still coated with bodies and blood of course) they find the cleanest place in the mansion (which later turns into Patchouli's library) and let Flandre rest there.
As soon as the next day came, they began cleaning up the mansion, Koakuma basically becomes the maid of the mansion, but Remilia still helped with the cleaning. Remilia had decided to store all of the blood into on place, so Patchouli used her magic to store it all in a single closet. This was enough blood to let both Remilia and Flandre last for hundreds of years.
When Flandre had finally woken up she almost immediately attempts going to the village again, but her injuries held her back. When Remilia sees this, she becomes afraid that Flandre has lost all sense of control, and will only attract stronger people that will eventually kill her. Fearing her sister's death, she decides to lock Flandre in a big room located in the basement of the mansion. She gets Patchouli to set up a barrier to keep Flandre in. (Day 1 of Flandre being locked in mansion)
Remilia heads back to the village herself to see the damage they have caused. She disguises herself as a human being and hides her wings under a cloak Koakuma makes for her.
There was a funeral being held for all the fallen at the massacre in the scarlet devil mansion. She attends to see the remains of the village, which is mostly women, children and elderly. There were only a few men.
Seeing this and the funeral, the words the assassin said during their fight made her feel sorry for the village. She wanted some way to attone for her and Flandre's sins, so she does the first thing that comes to mind.
Raise the assassin's child.
She asks around for where it is and a women sitting at the funeral had her in a basket. In the basket was also a pocketwatch that the assassin owned.
Remilia takes the basket and walks right in front of the memorial the humans made for the fallen and she apologizes to all the villagers without revealin her identity.
She tells them her resolve, that she will take in the assassin's child and raise her herself. She also promises to never attack the village again, and with that, she flew out the funeral. The villagers weren't even given time to realize she was the scarlet devil until she was gone.
With the help of Patchy and Koakuma, Remilia raised the child and gave her he name Sakuya Izayoi. Although patchy did help a little, Remilia attempted to raise her as independently as possible. Meanwhile, Flandre stayed locked in the room, while sometimes being fed by Koakuma and Patchouli. Remilia didn't even want to show her face to Flandre because she felt bad for what she had done, but also felt it was necessary to keep her safe.
As Sakuya grew a little older, The entire mansion had been cleaned out, and Oatchouli started building her library. Sakuya managed to get one of her books once and it was a picture book
about a maid. She couldn't actually read it, but the outfit the maid wore in the book fascinated her and she wanted to be just like her. Patchouli started teaching her how to read and write, she also taught Remilia since she didn't know either. (and Flandre too of course, but Flandre tries to look like she's ignoring Patchy when she does, but she actually pays attention).
When Sakuya is able to read the book she learns about everything the maid did to protect and serve her master, which only made her love the character more.
She eventually decides at a very young age to become Remilia's maid simply because she wanted to be that character. Remilia saw it as a joke, but she allows Sakuya to do maid work and even orders her around a little.
Years passed and Sakuya had grown to be a teenager, she was told that her parents had died in a war and Remilia, being friends of her parents, took her in. Remilia gave Sakuya her father's knives as a way to remember him by. Sakuya had actually become Remilia's maid and was able to replace Koakuma.
During all that time, many people had come to the mansion to fight Remilia, to get of the Scarlet Devil for almost murdering a whole village. Each time Remilia drove them out, but eventually Sakuya replaced Remilia and started driving them out herself.
Since Sakuya was the one kicking people out the mansion now, the scarlet devil rumor started to die out and the visitors became less frequent.
Around this time Sakuya had also began to master her time stopping ability. She slowed down her own aging in hopes to be Remilia's maid for as long as Remilia lives.
More years pass (make this somewhere around year 100 for Flandre being locked inside mansion, Sakuya never finds out about her too) and begins visiting Flandre herself, but only to give her food, she can't bring herself to say anything to her. Flandre herself only glares at Remilia everytime she comes in.
This goes on for about another hundred years, but Flandre never attacks Remilia, only glares at her. Remilia tries to lighten up the tension by bringing toys, but they
only get torn up by Flandre. Patchouli's barrier actually becomes ineffective at this time to after beig up for so long, but Flandre never notices since she never tries to get out anymore. (not that she tried a lot in the first place)
Around this time Hong Meiling shows up to the mansion shouting about how she heard a scarlet devil has practically massacred a whole village. (she's also extremely late on this news) She sees the scarlet devil as a worthy opponent and challenges her to a duel. Sakuya tries to kick her out, but Meiling holds her ground no matter how many knives she threw at her.
Even when she stops time Meiling predicts what Sakuya would do and eventually knocks her out.
This pisses Remilia off and they face off.
Just barely, Remilia wins. When Meiling recovers she thanks Remilia for the duel.
She acts like she goes away, but stays to sneak around the mansion. She ends up finding Flandre while she was sleeping.
Flandre interested Meiling, so the next day when Sakuya found her sleeping in one of the rooms in the mansion, she offers to become the gatekeeper to help keep any other people who might come uninvited away.
At first she's turned down, but people actually show up to kill the scarlet devil and Meiling kicks them out (literally), so she became the gatekeeper anyway. It turns out before Meiling arrived to te mansion she spread the news everywhere that she would fight the scarlet devil and the scarlet devil legend was born again.
While Meiling was gatekeeping she would secretly visit Flandre. Flandre would tell her how evil her sister is being, but when Meiling ignores it and tells Flandre about her fight with Remilia.
She tells Flandre about how she became a gatekeeper in a way that made it sound like Remilia sought out for her.
This actually fascinates Flandre, and Meiling keeps making up stories about Remilia each visit.
This goes on for a long time, Meiling blows up the story of how Remilia got fairies to work as maids. She tells Flandre that she saved a fairy princess and as a reward she got fairy maids, but in reality some fairies pissed Remilia off with a prank and she forces them to work as maids, but the fairies actually brag that they're working for a vampire and other fairies show up to work too.
Flandre grows to loke Meiling a lot and actually begins to idolize Remilia for all the fake stories Meiling tells her. Instead of glaring at Remilia when she visited with food she would smile and would no longer destroy the toys she brings.
This actually creeps out Remilia and she tries not to question it.
This goes on all the way up to year 495. By then, Remilia had moved the mansion to Gensokyo with Patchouli's help where shortly after the Vampire incident happens. Even though Meiling didn't know how it went down, she blew up the story about it to Flandre.
What Meiling did know about was the new spellcard rules for more fair fights. She hated these rules because she felt it went against her way of fighting, (and she was bad at it) but she teaches Flandre about it. Once the Scarlet Mist incident happens Meiling doesn't even try to stop Marisa when she came in. She hoped that she would run into Flandre too like she did. Reimu arrives shortly after Marisa and Meiling pretends to fight her when she comes by.
Marisa gets in a fight with Patchouli while Reimu runs into Sakuya, once both were defeated Reimu finds Remilia, when Sakuya tries to stop her Marisa fights her and allows Reimu to fight Remilia, and Reimu wins of course.
The party (or whatever happened) afterwards that Remilia attends with Sakuya at the Hakurei shrine happens and Marisa comes back to stea- I mean borrow some books, but finds Patchy trying to find Flandre who had broke after getting to excited since Meiling blew up the story yet again and she just couldn't stand by anymore.
Flandre runs into Marisa after Marisa beats Patchouli and challenges her to a spellcard duel. Marisa of course accepts it and does beat her, but Flandre had so much fun she tries for a rematch, but Marisa goes for the books while she still can and hightails it out of there.
Remilia and Sakuya return and LO AND BEHOLD FLANDRE! Remilia freaks out and wonders why she's out and about, but Flandre just hugs her, happy to hear her voice again. She tells Remi that she's gonna be strong and important like her one day and goes to challenge Meiling to a duel. She has forgotten all about why she was locked up in the first place.
Sakuya is confused, so Remilia explains that she has been in the basement all this time, but doesn't tell her about why. Sakuya doesn't asked since she feels it's too personal.
Remilia was of course confused that Flandre knew anything that has happened at all overtime and tries to ask, but Flandre only challenges Remilia to spellcard duels. These spellcard duels became Flandre's new obsession, and eventually pissed Remilia off about it. She constantly fights Flandre and ends up forgetting what she wanted to ask her. (like why the heck she even knows the rules).
Patchouli doesn't even bother looking into it, so no one finds out what Meiling has been doing this whole time.
Flandre still stays in the mansion most of the time since she doesn't know much about the world, and blowing up random things isn't funny. So she stays inside and learns from Patchouli and Meiling.
anyways, my take on how the whole things went down
tl:dr - i spent way to much time writing this
