They still haven't given an actual reason Tyuule chose to stay behind. Like... why? "Oh this bitch attacked me so I won't let myself be happy even if people are defending me"? I just can't wrap my head around what they're trying to get at with her choosing to be miserable when she literally keeps saying she WANTS to go with him. Just forced drama bs.
She has a broken spirit.
Sure, it may sound stupid at first, but she dealt with so much that a part of her thinks she is undeserving of salvation, it is pretty common.
Just before that, Furuta had just saved her from being gang raped... oh sure, you could say she turned it on those asshole, but can you imagine it... how it must be to be forced upon by people who only see you as a thing? And having to lower yourself to be a "deviant" at their level so that you can screw them over?
Yeah... it would be great if she went with him, but... she is just tired... and i think she wants to take one last thing in her own hands... after all he did to her, after the lies he spun to make even her people to hate her, do you think she will be at peace leaving Zorzal alive?
Revenge may be a sucker's game... but there are people that are deserving of it.
We can only hope she can find at least some happiness... if not, at least some peace.