Flashback
At one certain night, Vạn Thư was sleeping in her rent house, Yukari suddenly pulled out a Duality Brush hidden inside Vạn Thư's sleeve through the power of her boundaries portal.
By the time she woke up Yukari already returned it back to her sleeve before she could notice it. And thanks to that Yukari could replicate the Scroll of Illusionary Dimension by 'borrowing' her property and used the scroll to enter Hakoniwa on her own.
Yukari: (So my theory was right after all, there must be another version of me from Hakoniwa who is also a chosen librarian like Vạn Thư. The Scroll of Immortality, Scroll of Teleportation and other scrolls might had been written by that same person too)
Yukari thought of this theory while writing a replica scroll
End of Flashback
Vạn Thư arrived to Suzunaan again as she published the next chapter of Hakoniwa Records. Seeing that Kosuzu was being busy at organizing her books, she sat down and waited.
Mamizou: Can I borrow your ink brush?
Vạn Thư: Huh?
She showed her surprised face when Mamizou met her in Suzunaan asking to borrow her Duality Brush. Vạn Thư crossed her arm and warned her.
Vạn Thư: Don't you tell me you want to create a new scroll? Didn't I make it clear I wanted to retire from my librarian job?
Mamizou: Well, you would destroy that brush if you wanted to retire didn't it?
To her surprise Vạn Thư handled it to her with a sigh, while Mamizou knew it looked like a normal ink brush but it had a hidden capability inside it
Vạn Thư: I knew my words won't change you so I will let you experience it yourself.
No matter how much she tried to write the new scroll the ink brush never injected its magic
Vạn Thư: Do you understand why it didn't work? If you are not a chosen librarian of the Great Library of Hakoniwa or if you have no parallel version of those chosen librarians then you are not allowed to use this brush to create a new scroll nor burning it.
Vạn Thư then demonstrated it by writing it down to the scroll then the brush suddenly burned with flame which allowed her to burn that same scroll to ash.
Vạn Thư: This is the Duality Brush, it represent creation and destruction. A chosen librarian could create a new magical scroll with this brush but they could also burn it no matter if that librarian is out of magic or not.
The Legendary Crane created this relic as a way to deal with the issue that all librarians in Hakoniwa will eventually running out of magic if they keep creating and using the scrolls. The Crane knew there would be a time where the old scroll must be burned if they fell into the wrong hand.
The Duality Brush was an important part of the life of the librarians as it had been handled down by generation of librarians. A specialized tool for a specialized purpose
Mamizou: So you had been keeping it for more than a hundred years?
Vạn Thư: Exactly, I knew I must keep it as long as I'm alive. There are always unpredictable situation where a scroll felt into the wrong hand or somebody accidentally activated it. Even if I'm no longer a librarian I still have to prevent such event from happening.
Mamizou began to smoke her pipe while sitting in a tree that afternoon with her Tanuki minions
Mamizou: (A contradicting but interesting librarian, she wished to live in peace but she always had to be cautious about those Hakoniwan scrolls. A librarian that burn scrolls as much as guarding it)
Mamizou showed her amused look while looking into Vạn Thư who was walking on the street
Meanwhile at Hakoniwa, various magical creatures began to immigrate toward a new world created right inside Hakoniwa under a magical barrier which prevented the normal human from knowing its existence. Yukari also created various boundaries portals connecting to various location in Hakoniwa to accelerate the immigration process.
That world was being called as Kotou which means Isolated Island. The true reason why it was being called as 'an island' because they converted an empty island from Hakoniwa with no human presence except for wild animals in order to transform it into a livable place in the future.
Under the administration of Alternative Yukari, Legendary Crane and other Gods they began to organize and restructure Kotou into a new paradise for all magical beings from Hakoniwa and beyond.
Yukari from Gensokyo played an important part in this process as she had been instructing other to reshape the environment of Kotou into her own vision. Little that they knew she merely used them to her own interest.
Long ago Alternative Yukari had been waiting for the Crane to lose its influence over Hakoniwa as she wished to create a new isolated world to preserve the magical creatures in here as she knew those magical creatures are always at the disadvantage for being unable to act in the broad daylight.
She always criticized the Crane and the other Gods for favoring the normal human too much while neglecting the fact that the magical creatures are always at risk of being extinct.
With the creation of Kotou however it won't be a problem anymore as there would be no one to challenge her vision. Yet Yukari solution affected her plan because she had to work with those she once opposed to preserve Kotou. Still, her plan aligned with Yukari's plan so she decided to follow her plan even if she could sense Yukari didn't help them out of good deed.
Yuyuko: Ara ara since there are no human here we could use a swatch of land to create a new garden just like Hakugyokurou!
Yuyuko looked at the scenery Kotou in excitement. Youmu walked around and saw various magical creatures including the 1000 bird army were being busy in the construction process. Their goal was to create a whole new town in feudal Hakoniwan style within less than a week.
The Alternative Yukari and other Gods already began to chant their magic to create a massive barrier to cover the entire Kotou to hide their plan of building their new paradise.
Yuyuko: The foods in here were tasty!
Youmu rushed in panic as Yuyuko were stealing food which was meant to be used for the food storage of the new town! Both Yukari was having fun at the hot spring.
Alt Yukari: You intended to let your friend having a visit in here wasn't it?
Yukari: It would be a waste for not enjoying it.
Alt Yukari: Does managing Gensokyo really hard?
Yukari: It was easy if there are no incidents.
Alt Yukari: So it was really hard then.
Both of them showed an amused look while Youmu desperately tried to drag Yuyuko out of the food storage while the magical birds snarled in anger for the loss of their favorite bird food. Yakumo Ran and Chen also joined Yukari in the hot spring enjoying the night in Kotou.
So far the construction of Kotou worked in a good progress and all they needed was to transport a human village into here to finish their grand plan. Yukari looked into the sky with a mysterious smile.
The Crane showed a suspicious thought while the other Gods shared their doubt.
Legendary Crane: I could sense a very powerful presence from Yukari far beyond anything we saw before. Her power to consistently create a rift between the boundaries without relying on any scrolls violated the law of magic on Hakoniwa.
The second founder was much weaker than this parallel version because her magic could be depleted hence she couldn't make any risky move without alarming us. But with that Yukari I knew it would be a wiser move to work with her in the meantime as she could wipe us out if she wanted to.
The Crane began to teleport into Gensokyo again but suddenly a boundaries portal transported it back to the same place instantly!
Every other God showed their fear of Yukari power as she suddenly showed up behind them.
Legendary Crane: So I was right about you, you wanted to control this place!
Yukari: Your attempt to warn Vạn Thư is futile as the barrier of Kotou had been empowered with my power and it is impossible for any of you to escape it. Right now you must work with us for the benefit of everyone.
Legendary Crane: The benefit of everyone doesn't include the Hakoniwan heavenly beings like us!
Some of the Gods used their scrolls to attack her but Yukari quickly dismantled them by using her boundaries portals to steal those scrolls before they could act. Other tried to cast their spell through magical relic or through other means but her portals sucked all of it into her boundaries then returned back to them.
By the time Ran, Chen, Yuyuko and Youmu joined the fight it was already over in a sudden manner as none of them tried to use their full strength against each other. The Crane managed to convince other to stop fighting which surprised Yukari as she didn't see the Crane tried to fight against her.
Yukari: As my last warning I will show you one thing that you might feel familiar with.
Yukari pulled out a Duality Brush from her portal, the Gods showed their anger as she set the entire stack of stolen scrolls on fire!
Yukari: You created the Duality Brush to burn the potentially dangerous scrolls in order to prevent it from falling into the wrong hand. Yet you didn't realize one day that same brush will be used to destroy your own power. The magic of Hakoniwa relied too much on scrolls and it was easy for me to dismantle all of your power. Vạn Thư's arrival in Gensokyo helped me to get into here to turn my plan into a reality!
Since then they had to comply with Yukari as they knew it was impossible to defeat her after her demonstration of power. Yet they all knew Yukari couldn't be trusted anymore, despite of that the Crane still stood in front of her and cooperated with her.
Legendary Crane: The moment I teleported into Gensokyo I already guessed various beings like you were extremely powerful more than many of us. This was why when I saw your extension of power I knew the fight must not drag on or else the fate of Kotou and Hakoniwa will be in danger if you brought more dangerous beings into here. Still, make no mistake, we didn't trust you that much except for the affair of Kotou. We only stopped fighting against you this time, mark my words.
The Crane and other Gods gone away leaving Yukari and other behind. Still, it was a victory for both Yukari as none of them would ever try to interfere with each other business again.