I think the aspect that hurts the most about Nazumika's one-sided hatred situation is that Mika created it artificially and entirely on his own.
We see in Frozen Ice that Mika shows a very black and white worldview, anyone who isn't valkyrie is automatically his enemy. This shows how much Mika cares about Valkyrie. Mika is Valkyrie. He stops eating to save money for Valkyrie, he takes all these jobs to help Valkyrie, all he does or thinks or is, exists exclusively for the sake of Valkyrie.
And when he chooses to hate Nazuna it's because he believes this is what Valkyrie would do.
Except Shu loves Nito. Even in ! era you can see that Shu's brashness is a response fueled by betrayal, sorrow, not hatred. Shu has absolutely no reason for commanding Mika to hate people or to proclaim everyone as an imminent enemy, especially now that he's not the emperor anymore.
Sure, he's been hurt, but the whole point of the execution was that it taught Shu that sometimes his ideals weren't right, and now he is particularly weary of giving Mika any commands that can shape his worldview.
And Shu loves Nito. He'd never want Nazuna to be hurt again.
Mika's hatred, then, is entirely his own. It's not something Shu gives him, it's something Mika teaches himself, in spite of what Shu can or will say.