Story

Second Eruption
The Core of Thunder first formed when the Will of the Honkai gave it to Sirin during the Second Eruption, it was and dubbed the Gem of Conquest. Through Sirin the Core's Soul was supressed and the Authority was utilised many times. Thanks to the efforts of Anti-Entropy they were able to remove the Core from Sirin and get it far away to help defeat Sirin.
Nagazora
Once Cocolia found out about Raiden Mei having the unstable Stigma of Herrscher of Thunder she implanted the Core of Thunder into her to channel the power and prevent it from going haywire, the Soul of the Herrscher of Thunder now had a chance to awaken but the Soul within the Herrscher of Thunder Stigma imprinted in on it creating a copy that would observe Mei from within her shoes instead of from an outside view. Mei would later meet a girl named Kiana who chose to be kind to her, as a result the Herrscher gained a liking to her. A Honkai eruption would later happen in Nagazora and the Soul within the Core took control of Mei to become the Herrscher of Thunder, however after much destruction due to the fact that the Soul was supressed by Sirin, Mei was able to retake control of her body. After Kiana got hurt by a Honkai Beast the Herrscher Soul took control once again to protect Kiana but Kiana forcefully pushed back against the Herrscher so the Soul gave control back to Mei.
St. Freya
When Mei got to St. Freya she had Himeko implant a bomb next to her heart that would go off when the Herrscher power was used for too long, this would kill Mei and prevent the Herrscher from doing anything, as a result the Herrscher Soul chose to continue to walk the path with Mei but not show her face unless necessary. When the St. Freya dorms were attacked by a Welt Joyce clone Mei was knocked out so the Herrscher chose to take control to protect Mei and her friends. After a hard battle the Herrscher aided Kiana in defeating the clone before returning things to how they were before. When Kiana was hurt during the mission to capture the Anti-Entropy battleship the Selene the Herrscher took control for a second to defeat all the attacking Honkai Beasts to protect Kiana.
Battle of Schicksal
During the Battle of Schicksal Mei was who was working to save Kiana had Himeko disable to bomb by her heart so that she could utilise Herrscher powers in the struggle if needed. When Kiana separated Mei from everyone else she was revealed to be the Herrscher of the Void so the Herrscher of Thunder Soul helped Mei get free from the Herrscher of the Void before granting Mei full access to the Herrscher Core and aiding her in battle. After escaping the last battle with the Herrscher of the Void, Mei and the Herrscher of Thunder would find themselves in a battle with the Herrscher of the Void a second time. After a long battle the Herrscher of the Void came out on top and ripped the Core of Thunder from Mei which put Mei into cardiac arrest and removing the Herrscher of Thunder's ability to help.
Herrscher of the Void
After the Herrscher of the Void took the Core of Thunder she began using its Authority at will like her previous incarnation did. As a result the Herrscher of Thunder Soul was supressed once again and was unable to give aid to anyone in any way.
Second Nagazora Eruption
When Mei needed the power most in Nagazora she created a connection to the Core of Thunder through her Stigma. The Herrscher Soul agreed to let Mei become the True Herrscher of Thunder and reobtain the Core to save both Kiana and Mei's lives. Through the connection Mei made to the Core and the Core made to Mei, Mei was able to draw on the Authority of Thunder leading to the Core fading from Kiana and returning to Mei, and the leading to the Herrscher Soul being imprinted on and erased like agreed and Mei becoming the True Herrscher of Thunder. Mei with her new powers revived the dead Benares as a Honkai Beast of the Herrscher of Thunder, together Mei defeated all the invading Honkai Beasts and stopped the Eruption. Mei wanting to help save Kiana's life then chose to go work for World Serpent to find a way to stop the Honkai and save all Herrschers. After a battle with the disagreeing Kiana, Mei would show off her power before leaving to go with Kevin to World Serpent.
Herrscher of Ice
Now working for World Serpent, Mei was sent on a mission to the destroyed Coral City with Owl and Raven to deal with the Fifth Honkai Eruption and the newly born Herrscher of Ice. After fighting through Honkai Beasts and finding the Herrscher of Ice Owl betrayed the group by knocking out Raven and stealing her Divine Key, then by using the suppressors they had to stop the Herrscher's powers on Mei, then running off with the Herrscher of Ice in an attempt to save her. After catching up with the Herrscher of Ice and Owl, Mei fought with them and defeated them, Raven reclaimed her Divine Key and Mei put her sword through the Herrscher of Ice to kill her. At that moment the Core of Stars formed within Owl making him the Herrscher of Stars, this wouldn't last though as he immediately gave up his Core to Ana to make her the Herrscher of Rimestar. After meeting up with Durandal, Mei and Durandal joined together to fight the Herrscher of Rimestar. After a battle with the Herrscher of Rimestar she was defeated, allowing Mei to use an emulated and increased version of the suppression devices through her powers to stop the Herrscher of Rimestar's powers and put the Cores in a suspended state.
Herrscher of Dominance

Elysian Realm

Kolosten

Herrscher of Corruption

Project Stigma