[SPOILERS] Stormblood Ending

[Theodric]

Yotsuyu surviving doesn't bother me in the slightest. Yes, she did terrible things - but she did them due to being treated terribly by the Doman people who were far from innocent themselves. It's a sharp contrast to Hien's self righteous belief that liberating Doma is completely justified and his people are perfect and flawless. He even seemed unnerved by her revelation. She's essentially a survivor of abuse, thus serves the role of a tragic antagonist very well.

As for a 'redemption' arc, that remains to be seen. If someone like Yotsuyu can be redeemed, though, then that actually works in favour of a more interesting story moving forward. We've already seen the protagonists drown numerous Imperial troops to win a key battle so anyone who believes that things are as simple as 'good guys' and 'bad guys' needs to pay more attention to the story. Drowning is, after all, one of the most horrific ways for somebody to die and far from honourable. Imagine the self righteous anger from the leaders of the Eorzean Alliance if it were their troops who were the ones drowning?

In short, there's likely more to Yotsuyu's tale and the game stands to be much more interesting if the approach to characters isn't 'kill them off if they're not nice or do something horrible'. I mean, think about all the horrific stuff that Kuja and Beatrix did back in FFIX and then look at how their stories ended up playing out.