>>2345099I'm not so sure, Ryuko cares so much about Senketsu he's tethered to her heart, I think that's what Nui wanted but couldn't achieve. Nobody ever cared for her so she entrusted herself to Ragyo, but Ragyo doesn't love or hate her, she's just a tool. It's Nui's tragedy, a lonely soul who doesn't understand love, and can't make it by on hate, literally doomed to obscurity.
If Nui came back it has to be through some other means, or maybe a copy.