Thanks. This leans more folkloric, mythological than outright transsexuality, IMO, especially in the politico-pandering definition we see more from Western developers; much like the honey badger, I don't think Japanese developers give any Fs.
In my reading, I liked below relevant overview of the lore:
After Godfrey's banishment from the Lands Between, Marika took Radagon as second husband and King Consort, elevating him to become the second Elden Lord. Radagon already had three children with Queen Rennala of the Carian Royal Family, and after his union with Marika, she would raise her new step-children Radahn, Rykard and Ranni to demigod status.
Marika and Radagon would go on to have two more children of their own, the twins Malenia and Miquella, who like Marika herself and Radagon's daughter Ranni, were Empyreans, and were thus potential successors to Marika. However, Radagon and Marika were in truth one and the same, in fact Radagon was described as Marika's male "other self". Thus the twins were the children of a single god, and they were both born afflicted: Malenia with rotting sickness and Miquella with eternal childhood.