Skyrim: Azura and Nocturnal
Azura and Nocturnal combine in this quest to undo the work of Clavicus Vile. Alone, neither would have been able to do so.
Azura was depicted in TES II:Daggerfall as a topless woman dressed in a blue skirt, in a style that was repeated in her statue in both TES III:Morrowind and Tes IV:Oblivion. TES V:Skyrim covered her up a bit, at least for her statue, and she does not make any personal appearances.
She consistently wears a garland of flowers around her head in all the games. She retains that even with her Succubus outfit, which also uses her preferred shade of blue.
Nocturnal's image in Daggerfall and Oblivion had her half-covered in a cape. My mod "Evergloam" for Oblivion, pulled her cape back to reveal her topless underneath it. This conforms to the style suggested in the book "Purloined Shadows", Skyrim covered her up (again) but not too much, leaving it clear that she likes to be admired.
In Skyrim, she was a pale Redguard, and ESO has her a few shades darker. My take is that she changes her skin shade as often as her outfit. Her hair seems to be consistently black.
Her Succubus outfit is red, for contrast.
The two consider each other sisters, which makes them closer than most other Daedric Princes, but there is the usual sibling rivalry in much of what they do. They will often compete, but rarely with any malice.