I have a different theory for the origins of the Danaan 🔥 name (and for Rhysand's last name.)
People theorize Rhysand's family name might be shared with those of Crescent City. To begin, I don't think this makes sense. He's a descendant of Silene, Theia's daughter who married a High Lord of Night and stayed in Prythian. According to patriarchal rules, Silene's descendants would've acquired that HL's name. Unless Fae from what is nowadays Night also fled to Midgard (which looks like it happened), like some of what is nowadays Autumn did. Pelias origins are sus...
But many believe Rhysand's surname might be Danaan because it's constantly repeated how he resembles Ruhn, well, Ruhn Danaan. Not just looks, they have the same magical powers, even daemanti abilities. BUT, we need to remember that Ruhn doesn't get any of this from his father, Einar Danaan, he gets all of this from his mother, Lorin DONNALL! He is a disappointment to his father from both not carrying enough starlight nor his fire!
Lorin is the daughter of a prominent noble house that had defected from Avallen's court. Lorin's mother was a Donnall. When the Autumn King decided after a few centuries of ruling that he wanted an heir, Lorin was selected for one purpose, breeding.
Her deep blue eyes are the same color as Ruhn's and hold a sadness in them. Lorin has a beautiful, delicate face and silken black hair.
Due to her heritage, Lorin should be a telepath, meaning she can communicate with people via their minds, also called mind-speaking. However, she can't read their thoughts.
Also due to her heritage, Lorin should have the ability to manipulate shadows. This includes summoning and walking through them, and cloaking herself and others in darkness.
In Crescent City, the Fae related to shadow powers and daemanti abilities are the Avallen Fae, so, the Donnall line.
The Avallen Fae are known for their shadow magic. It is the power to summon shadows or mist that can not only veil the physical world, but the mind as well. They can also have telepathy.
So, who are the Danaans? From the Valbaran fae?
Fire magic is a common power among the Valbaran Fae
Einar Danaan was the ruler of Lunathion's Fae, the Valbaran fae. ALSO KNOWN AS AUTUMN KING. AUTUMN KING without any APPARENT connection to the concept of Autumn, whatsoever. He has RED HAIR and AMBER eyes. His power are FIRE.
Einar could create, use, and control fire. Due to his age and status, Einar was incredibly powerful.
So no, I don't think Rhysand is a Danaan, most likely a Donnall. But do you know who might he a Danaan? THE AUTUMN LADY!
Hear me out. The Autumn King, Einar Danaan, is clearly related to what nowadays is the Autumn Court in Prythian.
He probably comes from a line that proceeds the Vanserras or was/is parallel to the Vanserras.
The Autumn Lady comes from a powerful family of fire yielders. She and Einar can be descendants of the same line! They can be related! (Although, at this point, everyone from Night, Dusk, Autumn, Avallen and Valbara are kinda related)