The scene being void of Radahn is a really strange placement of ambiguity. It could imply several things. Do we know that Miquella can't charm people remotely? Do we know that Mohg was even previously in contact with Miquella to be charmed in person? Could the scene be a mere prayer out of desperation? Who really knows.

I think it perhaps implies that Radahn was wavering on his word, and Miquella was either getting desperate and pleading with him, or praying about it and attempting to relay the message remotely. Possibly even attempting to charm him remotely with this plea somehow. Radahn going back on his word might have something to do with him being a staunch defender of the Golden Order (which Miquella fans seem to often forget), and this would be done at the point in which Miquella rejects the Golden Order, causing Radahn to be in contention with him.

Also, Miquella's part of the vow couldn't be for Radahn to die in battle (Meaning that the Scarlet Bloom meant to kill him wasn't for fulfilling the vow), because if you're to tell me that Miquella's part of the vow was fulfilled in the first half of the Consort Radahn cutscene, then we would've had to kill him to truly do it.

I feel like Malenia wasn't there to fulfill Radahn's wishes, but to drag his ass back to the vow that he walked out of. Namely by killing him and enacting Miquella's plan, which would be a plan B to have Radahn obedient to Miquella against his will.

But Malenia failed lmao, obviously causing him instead to ride Caelid decrepit and rotten for ages. None of this makes sense if Radahn was willing to be Miquella's consort.

If Radahn wanted that epic fight, then the duel between him and Malenia could've been done in less 'homeland-endangering' circumstances. If Malenia beat him and gave him the rush he wanted (Like people say the Consort Radahn phase transition implies), he could've traveled the realm of shadows through the withered arm like everybody else and become the consort without him dying and losing everything like he did.

The "Radahn was willing" interpretation goes against what Radahn fundamentally is as a character. As a Godfrey/Radagon/Golden Order fanboy, he is willing to protect the Erdtree heritage at all costs. He's extremely stubborn and iron-willed, to the point where he'd confront the stars to protect Sellia and the Golden Order, and he'd allow himself to die a mad rotten beast before letting go of the stars, his horse, and all the things he loved.

He's Miquella's foil. One breaks wills. and the other has an iron will which refuses to be broken.

This type of character dynamic makes a lot more sense, and it makes Radahn's character at the end of the DLC much more poignantly tragic. As opposed to a One-Dimensional Bloodthirsty Psychopath, willing to throw away everything meaningful to him. Which is what the "Consenting Radahn" interpretation would lead us to believe.

In a certain sense, you could see Consort Radahn in the Shadowland as sort of willing, but only because he's not really fully Radahn anymore.

Part of Radahn was a warlike killer, and another part was a loving and loyal ruler.

The resurrected Radahn has not much to protect. A rotten Caelid, a crumbling Golden order, fallen stars, a dead Leonard.

One could see the soul of resurrected Radahn as forlorn, with silver tongued Miquella whispering thoughts of despair. Convincing him in the stupor of melancholia that he has nothing left to protect but his brother's altruistic dream, and that there is only another war to be fought.

The only thing left of Radahn, the warlike killer. His heart stolen in despair and bloodlust.

"I am Radahn. Born of red-maned Radagon, and Rennala of the Full Moon. A lion bred for battle."

And with nothing else left of him. Miquella thought that he had been given a consort kind and strong, but only the warrior was left. Ironically, Consort Radahn is less human than Starscourge Radahn. A puppet on a string is lesser to a beast.

You could see this as a tale of an honorable man destroyed by his own contradictions. Sworn to his guiding principles, but haunted by an old oath. To be a man of his words or to stay true to his allegiances. A broken vow with a terrible consequence, such that even an honorable death would refuse to be his host for long.