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I honestly don't think Morgan ever beared any ill will towards Castoria. I don't think she's ever directly attacked her before Castoria rung the first bell (her followers might have of their own volutions but Morgan herself didn't give any order) and it's never stated what Morgan had expected Woodwose to do upon reaching Tintagel. But most importantly I am thinking about "Daughter of Tintagel. So long as you remain Artoria, I do not see you as an enemy." Morgan is intimately aware of the cruelty that awaits the child of prophecy should she choose to take that mantle. She’s giving Castoria an out. We don’t have to fight. We don’t have to fight. If you want to leave I will let you if you want to live I will let you. And when Castoria doesn’t back away Morgan makes sure to tell her that Castoria is justified in killing her, that any blood shed while fighting her would not be Castoria’s sin. We stand on opposite side of this war we chose to protect different things but ultimately we are the same and as such I cannot hate you. Morgan is a Saber forced into the role of a Sakura, Castoria is a Sakura forced into the role of a Saber, and while the nuance is important they are also both very much the same.