Hi , I don't know if you answered this yet but what do you think about the theories circulating in the english lore community about Marika being behind the Night of the Black Knives? Maliketh's Remembrance and Black Knife armor are often brought as proof. I find this theory to have no basis in the lore, but it would be nice to hear your opinion.
(If red-black particle in Marika’s body is a stolen fragment of Rune of Death it means that Marika/Radagon had their hands in Night of Black Knives)
So far my main theory is that Marika was behind Night of Black Knives, but the outcome was not what she wanted. My main evidence is how おお、永遠の女王マリカよ。貴女の、醜い落とし子を抱いてcertain ghost speaks about Marika's unwanted children. 落とし子 is a prime example of usage of keywords in JP script.
落とし子 in Elden Ring describes (failed) children which were born or created from rituals or magic. I've been already touching this subject in a post about Omens. A good example of "unwanted" child is Sellen's graven-mass. She aimed for the creation of "starry" child, merged herself with Azur and Lusat (ritual), failed it and the result was a meatball (unwanted bastard child). Interesting, that Zorayas, another 落とし子 created from Rykard's experiments, complains that she was "born not from grace", which is true for the rest of known 落とし子 - Astel, Bastard of the Void, and Kindred of Rot. Maybe there is a connection or maybe there is not, even though we know about existance of the graceless royalty (Roderika), it's hard to believe that Godwyn, the most famous victim and Marika's son was graceless too.
However, before jumping on the idea that demigods, who died during NoBK were hideous abominations born from weird magic, let's consider that the core part of Night of Black Knives is a ritual.
I stole a fragment of the Rune of Death, and used it to forge the godslaying black knives through fearsome rite (Ranni)
A ritual performed on the oddly misshapen blade imbued it with the power of the stolen Rune of Death (Black Knife)
Maybe Marika for some godforsaken reason decided to kill Godwyn for good (I strongly suspect that worship of ancient dragons, a race that previously owned Elden Ring, is what costed Godwyn his life; you aren't estabilishing your little cute cult around your scalie friends, when your mom is one and only god) and collaborated with Ranni, who forged godslaying Black Knives. But Ranni hijacked her plan and broke cursemark in half, therefore Godwyn and demigods weren't killed properly and became 落とし子
However, it raises obvious question: why would Marika, a giant perfectionist, collaborate with a daughter of woman, who lost her mind after divorce, and, to no ones surprise, betrayed her?
I mean, even if we go with popular "Marika wanted to destroy Golden Order from within and help Ranni" it doesn't explain why Black Knives became enemies of Ranni's group in the main game.
Description of NoBK from official bamco site also provides some interesting info:
One grim night in the depths of winter, a flock of unknown assassins stole across the Lands Between. In a coetaneous attack, this foul covenant snuffed out the lives of many of the God-Queen’s kin throughout the empire, too numerous and too scattered for her godly protection to save.
I mean, I can theorize why Godwyn was chosen as target, but what about the rest? Or maybe there was no target at all and Black Knives attacked chaotically and Godwyn was a collateral damage?
After all, I don't deny the possibility that Ranni "did it all". I even have a crack theory that she collaborated with Radagon and maybe one day I will post it, but I need to post my general write ups about him first. Another wild idea is Ranni's alliance with the outer god of deathbirds or its followers, considering how NoBK restored lost sorcery of death. Honestly, along with Marika/Radagon's motivations it's the most lore convoluted event in entire game.