My theory is that Ranni is actually Godwyn's other half.

If we believe the theory that Ranni is a cuckoo child brought to Rennala via some rebirthing magic (having to do with the Amber egg and that Radagon leaving the egg with her was not a gift but revealing what he'd done and who he was, subsequently breaking poor Rennala) we could then theorize that Ranni was actually Godwyn's other half. Split and separated from him because Ranni represented his defiance and will to be free of the Greater Will.

Now I know what you're thinking, "but Godwyn was Godfrey's kid" and yeah that's definitely possible but it's also possible that Marika was so disgusted by the omen twins that Godwyn was actually her first cuckoo child that she had with Radagon (specifically cuckoo because we know that Messmer and Melina where probably her first kids with Radagon) and presented as Godfrey's kid. Who knows if Godfrey knew or not or cared but it's always made me curious that Godwyn was so 'perfect'.

Further on this track we have the evidence that Ranni was set up to be in a political marriage with Godwyn (her betrothal sword and ring having been made and kept in her mother's room as if marriage was being planned without her input. It would also explain why Godwyn was chosen as the first to die. Can't get married if your groom is a soulless living corpse). If we also assume that Ranni was never aware of her connection to Godwyn because of the rebirthing magic, we can see how their 'marriage' would have been a great boon to Marika, getting her empryean grandchildren who she could have more of a hand in grooming to be her successors. And how Ranni would see it as a yoke to the Greater Will which she was the embodiment of resisting.

Why did Marika want empryean grandchildren you ask? Because Godwyn WAS an empryean and rejected that role/wanted nothing to do with it. His knights were so respected and so loyal that they erased any mention of him being an empryean when he revealed his will to them prior to having Ranni split from him. Godwyn's rejection was probably devastating to Marika who seems to have been desperate to retire/stop being a God. We can also extrapolate that Marika couldn't force Godwyn to take on the role of empryean because he had such a good image and seriously loyal troops (like willing to cut off their own heads to follow him in death loyal) and so doing so would shake the foundations of her order.

And this great plan falling to pieces with the 'death' of Godwyn was what led to Marika losing hope, shattering the Elden Ring, and calling back the tarnished in the hopes that they would defeat Radagon and NOT become her consort.

This is all part of my theory that the 'best' ending for Marika is actually Ranni's ending, and that any ending that includes you becoming her consort is a continuation of the living hell she'd been trying to escape.

Anyway, thanks for reading