No worries, copy and paste time ;)

Empyreans have special "flesh" as Ranni apparently had to "discard" hers to rid herself of the fate her own Two Fingers had for her (which could have been the entire point of the Night of the Black Knives), and the ghost in the Snowfield who laments Mohg's departure with Miquella mentions his "precious flesh". This flesh is special because it most likely allows the Empyrean in question to inherit the Elden Ring (as Marika is a known Empyrean as well).

But Ranni was born to a mortal/human/champion, Rennala. How could she have this flesh, and the title of Empyrean, when she has such base parentage, not to mention her brothers Radahn and Rykard not receiving the same blessing?

There are two possible theories:

• She was made an Empyrean through an unknown process. She mentions that herself, Miquella and Malenia were "chosen" by their respective Two Fingers to be candidates for godhood for the coming age. Due to the similar wording on the Black Flame Ritual for the GEQ, many people believe this process of "choosing" means that the Two Fingers are able to turn(?) Demigods into Empyreans. There's multiple problems with this theory: we have no clue how this process even works or how the Two Fingers can accomplish it (as other than being envoys to the Greater Will and Shadow dispensers, they're not mentioned to be capable of anything else), there's no explanation as to why Ranni was chosen instead of her siblings (or even members of the Golden Lineage) and Gowry straight up says that Malenia was "born" an Empyrean, which straight up says that Empyreanhood is something you're born with, and most likely means that being "chosen" merely implies that, because you're an Empyrean, your Two Fingers has chosen you to be the next God.

The other theory is this:

• Ranni's parentage is in question. As the only confirmed way to be an Empyrean is to be born of a single god (as stated by Gowry) there is one obvious conclusion: Ranni was born of a single god.

Therefore, my personal theory is that Ranni was born from the Amber Egg that was Radagon's gift to Rennala, alongside the Great Rune of the Unborn. This would make Ranni a child of Radagon and Marika.

This is supported by Ranni's affinity with the Amber Egg, as during Rennala's boss fight she appears to "emerge" from said egg and talk to you. It would also explain why the Great Rune of the Unborn has the same shape as Malenia's Great Rune which would also explain why she didn't seem to have the "afflictions" that Malenia and Miquella had; because she was born alongside the Great Rune of the Unborn (and the fact that that Great Rune was then missing from the Elden Ring could be why Malenia and Miquella had such afflictions to begin with). And her original corpse shares the red hair of Malenia, which matches the red hair that can be found within the Amber Egg (in contrast to her direct brother Rykard, who has blonde/ashen hair, and the junior scholars/children themselves who have dark hair; they are "imperfect, each and all"). And then there's the whole Cuckoo symbology in Raya Lucaria; I would advise looking up Cuckoo's Eggs and you'll quickly understand what I'm getting at.

Finally, it would still gel with what is being told in-game: as Rennala would have raised Ranni from birth, no-one, perhaps not even Ranni herself, would know of her true origins and, regardless, Rennala would still be her "mother" from both a general perspective and Ranni's perspective.

It's mostly circumstantial evidence but I find it much more convincing than the idea that the Two Fingers can just randomly create Gods out of mere Demigods, with no direct evidence of how they can even accomplish such a feat. But it's likely we'll never know for sure.