Justice? I'm not sure how much the dead care about justice.

[She shudders as she speaks. As much as she claims otherwise, more than once she's sought justice herself. For Haurchefant. For Ysayle. But the truth has weight beyond justice, and it appears that Shirou's very much aware of that.]

But the living are another matter. If this is Celestia's doing, I don't doubt it could happen again. You're correct--there's an answer somewhere here and we need to find it. Where do you suppose we start?