After the event in Doma's Castle, Yotsuyu lost her memories and became entirely a different person. By living beside Gosetsu, she learnt the warmth of parental love.
In a sense, it was Heaven's way to give her a second chance, a way to redeem herself.
During the events of 4.3, she finally regain her memories, while encountering both of her adoptive parents. Thus she is confronted by a decisive choice :
- She either go back to the Castle, where Gosetsu and Hien are and face her judgement. Then she eventually got traded in exchange for the prisoners, but their is a definitive possibility that she could stay, protected by Gosetsu, and spent the rest of her life trying to right her wrongs.
* Or she give in to her desire of vengeance. Rejecting by the same way her redemption.
Of course, if you have played the 4.3 scenario, you know how it ends. Yotsuyu have killed both of her parents, thus sealing her fate. She rejected everything, even Gosetsu, and even her humanity by becoming a primal, for the sake of revenge.
During the fight against Tsukuyomi, we see her fear attacking her. Her parents, the domian, her brother, etc... We tried to protect her from this, but we would have failed if Gosetsu's image didn't block Zenos' shadow.
And I think this is were it show our failure as Warrior of Light. Because her only image of a "virtuous person" was the old samurai. He was the only light in her heart, the only rempart against her worst fear.
At no point, an image of the Warrior of Light appear to help her. Or perhaps you could say that Gosetsu was her Warrior of Light?
He was the only one who accepted everything of her, even the Yotsuyu before she lost her memories, and still cared for her.
Just think about it : The Empire either want her dead or want to use her like a tool. Hien want to use her like some exchange money if she got her memories back, while Yugiri just want her head.
And us, the warriors of light, are just standing here, hoping that she don't regain her memories so that Gosetsu stay happy. Or worse, that she regain her memories, so that
something happen.
But at the end of the battle,we found at our feet the corpses of a brother and his sister, after they killed each other. And a grieving Gosetsu.
Some Warrior a Light we are, right?
I wonder what make us so different from Zenos, right now? This event showed us that we are no messiah, but just an overpowered killing machine, striving for the next battle that will make us feeling alive.