Hello everyone, I've just completed the DLC twice and have a thorough understanding of its lore. I'll be discussing spoilers, so proceed at your own risk.
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From Freja's quest, we know that Miquella asked Radahn to be his consort, but Radahn initially refused. Despite this, Miquella insisted on a vow that if he ever achieved godhood, Radahn would become his consort, to which Radahn eventually agreed.
Knowing Radahn was crucial for his path to godhood and driven by his desire to create a gentler world, Miquella didn't accept Radahn's refusal. He tasked his sister Malenia to confront Radahn, but Malenia failed and inadvertently rendered Radahn's body unsuitable to be Miquella's consort.
Undeterred, Miquella turned to another approach: using his power to charm his brother Mohg into kidnapping himself from his cocoon.
That's why Malenia didn't search for her brother; she already knew his location and opted to wait for him at the foot of the Hailgtree.
Before Mohg kidnapped Miquella, Miquella charmed the strongest fighters to search for him, intending to kill Mohg and use his body to revive Radahn, whose original body had been corrupted by Malenia rot.
After defeating both Radahn and Mohg, Miquella acquired Radahn's soul and Mohg's body, initiating the process to revive Radahn in Mohg's body.
(From here, my speculation may be inaccurate.)
During Miquella's journey in the land of shadow, he began to undergo a transformation and the one who noticed this transformation was none other than miquella other self St. Trina. St. Trina understood that achieving godhood would trap Miquella within the greater will's influence. Ranni's quest revealed that an Empyrean body becomes enslaved to the greater will, leading Ranni to abandon her body to avoid this fate.
Despite St. Trina's warnings, Miquella refused to listen, causing a conflict between them. This conflict led Miquella to abandon their former self, as he quote, "I abandoned here my love."
Now, we must intervene to stop Miquella and offer him forgiveness.
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Having completed the DLC's plot and lore, it has disrupted my plans for this fanfic. As you know, I intended to revive Radahn for a future storyline, but currently, it seems impossible as Radahn's soul is not in his original body. Without Radahn, the entire fanfic faces an uncertain future, but rest assured, I won't abandon it.
I see two options:
1. Revive Radahn somehow, but exclude the DLC part from this fanfic.
2. Do not revive Radahn, include the DLC part, and accept the possibility of a realistic, potentially bad ending for the fanfic. (I might find a way to prevent this.)
Please vote for one option, as I won't upload a new chapter until everything is confirmed and the story progresses smoothly.
Additionally, after completing this fanfic, I may write a Kingdom anime/manga fanfic, as Kingdom is currently my favorite anime/manga series.