Story

Backdoor
When Mei got trapped by Project Stigma her connection to the Signets of the Flame-Chasers allowed fir Viil-V's backdoor system to activate, resulting in Elysia showing up in Mei's dream based on her memories to guide her to cracks in the dream that would allow Mei to realise her situation and escape the dream. After Mei realised she was in a dream and found all the cracks, she was able to get a compass that connected to her Herrscher Core. Mei was then broken free from the dream by Senti.
Locating Origin
With the compass in hand Mei noticed that it was acting as a beacon and was sending a signal from her Herrscher Core. Thanks to her trust in Vill-V she trusted the signal and believed it would bring her to the Authority of Origin that had previously stood up against Finality in the Previous Era in the form of Elysia. As a result a plan was formed to follow the signal and obtain the Authority of Origin to help in the fight. To pursue the signal Mei and Bronya entered the Planet Directory of Project Stigma, relying on Kiana to break them free once they were done. After getting ready they realised that Kiana followed them in so she can located them where ever to get them out without problems. While traveling through the Planet Directory towards where the signal was going Mei found herself going down a path she had to go down alone, as a result she ended up at a strange train station. After working on going forward to find the Land of Origin it kept getting further and further away, as Mei stopped trying the beacon spun up and the voice of Vill-V came out, to Mei's disappointment it was seemingly just a message to the long gone Elysia. As Mei gave up she heard another familiar voice, and she found Raven standing around watching her. After a conversation and a battle with Raven the Gray Serpent managing Project Stigma appeared and put Mei to sleep, trapping her in the Stigma of the Herrscher of Thunder. Now stuck in the Stigma, Mei had to relive memories and how things could have been different. Noticing that things were not right Mei confronted the her Stigma Soul who was behind it. After confronting the Stigma Soul in a conversation and battle, the Stigma Soul broke Mei free from the Stigma, returning her to the Planet Directory. Now back in the Planet Directory, Mei fight off some Imaginary Constructs and confronted the Gray Serpent who trapped her in her Stigma. After a conversation of goals and a chase Mei took on the Husk Existentialism Construct and before confronting the Gray Serpent again who suddenly died. After that the beacon activated again, creating a crack in space leading back to the train station. After being in the train station again Mei was transported to a strange area where she faced her inner struggles. After facing them, Mei came together with them and continued on, eventually coming to a stop and calling out Elysia's name, leading to the Land of Origin and a form of Elysia appearing.
Birth
Now being in the Land of Origin with this Elysia, Mei found out the truth about the situation, and that the Elysia before her was born from her memories being accessed by the Authority of Origin to form a suitable form for interaction. After changing the scenery to that of the Elysian Realm, Mei and Elysia had a conversation where Mei told Elysia everything about her friends and what was going on. Knowing that it couldn't last Mei and Elysia returned to the Land of Origin to let Mei become the Herrscher of Origin. Not knowing how it will go down Mei asked Elysia, who revealed that the Authority of Origin had been within Mei latched onto her Herrscher Core since she entered the Land of Origin, already making her the Herrscher of Origin. To give it a spectacle and to give herself a send off to Mei, Elysia gave Mei a metaphorical push forward and awakened the Authority of Origin within her, leading to Mei taking on a new form as the Current Era Herrscher of Origin, and Elysia disappearing for good. After thanking Elysia Mei left the Land of Orign and returned to the train station before going back to the Planet Directory to find Kiana and Bronya.
Seizing Finality
Due to not having a way back to Kiana and Bronya, Mei chose to follow a mysterious power she felt, hoping it would lead to them. As a result she met back up with Kiana and Bronya who had been following the power of the Herrscher of Origin. After recounting events and sharing information, the group got in contact with everyone else through Senti which allowed them all to put a plan together for creating an artificial Herrscher of Finality. Once the location of the Cocoon of Finality was located, Mei used the Authority of Origin to link together the Authorities and strength of Kiana, Bronya, Senti, and herself to attempt to make them all Herrschers of Finality, however since Kiana was the closest to the Herrscher of Finality the Cocoon of Finality only allowed her to ascend the to Herrscher of Finality. Due to still being linked to Kiana and Bronya through the Authority of Origin, Mei and Bronya gained strength and power through Kiana's new power, finally putting them in a position to face and defeat Kevin in battle.
The Final Battle
After making her way to Kevin with Kiana and Bronya by her side, the group challenged Kevin to a battle to put an end to all of it. Kevin started the battle by going on top of a Honkai Beast he created named This Worldly Beast, an embodiment of each era of history, splitting up Kiana, Mei, and Bronya in the process. Mei held her own against the Mesozoic Era: Chimera's System arm, eventually after Kiana defeated the Paleozoic Era: Leviathan's Onlooking arm, she gave support to Mei allowing the two to defeat the Mesozoic Era: Chimera's System arm easily. Once it fell the two rushed over to help Bronya take down the final arm, the Neozoic Era: Diabolical Transcendence arm. Once all arms were defeated the This Worldly Beast was immobilised leading Kevin to start attacking with debris from the battlefield. After the group cut through all the debris Kiana struck the final blow and destroyed the This Worldly Beast, passing what Kevin called the diabolic test. Kevin then unleashed and joined with the signet of Deliverance, entering a new form and that utilised all his power including the power from the Authority of Finality he held, and challenged Kiana, Mei and Bronya to a fight. After a long fight where Kevin utilised all his abilities, Kevin put up a strong shield that prevented any attack from getting to him. Mei, Bronya and Kiana with the help of the Hyperion and the hopes and strength of everyone, were able to overcome the shield to regain the ability to deal damage to Kevin. After final efforts put in by both sides, Mei cut through Kevin with her blades, Bronya crushed him with a spear, and Kiana was able to deal the final blow with her sword and defeat Kevin. After this Kevin and Kiana vanished leaving a confused worried Mei and Bronya. Mei and Bronya were then reached out to by Kiana who then explained the situation. After this Kiana put out a message to all humanity but in the process cut the vocal connection from Mei and Bronya again leaving them to once again be confused and worried. After a while Kiana showed up to Mei and Bronya to say her goodbyes. Bronya and Kiana agreed to chat and play video games together, and somehow Mei got roped into joining them despite being bad at video games. Mei and Kiana then went for a walk together, talking about their futures and past, leading to Mei revealing to Kiana that she wishes to become a teacher. The conversation of the two is cut short though as the train of destiny arrived to take Kiana to the Cocoon of Finality to play out her role, leaving Mei to return to earth on her own.
Herrscher of Finality
Once Kiana made the choice to become an artificial Herrscher of Finality she drew the Authorities from all the Cores with help of the Herrscher of Origin, through this she was able to get close enough to the Herrscher of Finality that the Cocoon of Finality granted her access to the Authority of Finality. Due to being artificial Kiana continued to require use of all other Authorities to wield the Authority of Finality, so the Core of Thunder was pulled to Kiana to keep the connection alive. Since the Authority of Origin was latched onto the Core of Thunder it was pulled to Kiana along with the Core of Thunder.