@Aichan
That's the point. He
has no legitimacy. Unless the
empire itself acknowledges him, or he utterly defeats them (history is written by the victor), any attack on the empire is
unlawful. The empire just has to
not accept any declaration. If MC has other allies,
they might legitimize him in their eyes,
but not within the empire.
Read their conversation again. I think you'll find that what she
actually said amounts to "don't do it",
not "wait". You're reading more into it than what was actually said. There was nothing about doing it later, it was
all about an attack (at all, not just now) fucking things up for MC. Nothing about war, only about stopping the death of the emperor. She told him to stop for the sake of international relations, offering
no alternative route to retribution. She
almost literally told him peace outweighs family. Family is nothing compared to order being upheld, thus it logically follows that family is expendable for the sake of peace.
It is literally her whole argument. I'm not saying it's wrong, I'm just saying you need to acknowledge that's what it actually
is.