Like if a bug was a girl

In both ALNST and ZOMST, Mizi is in an abusive situation that causes her harm both physically and mentally. In ALNST, it's largely due to negligence and lack of understanding or proper care for her at the hands of Shine. In ZOMST, it seems to be at the hands of a mother who takes out her frustrations on her, however apologetic she may or may not be after the act. In both ALNST and ZOMST, she has the same issue as a result: she doesn't want to be seen as small. Treated as lesser. Seen as cute, or as some decoration, or pitied. When her options are crush or be crushed, she wants control, which leads to a lot of dysfunction in her relationships with other people, but especially with Sua.

Not some pet you keep around the house, huh?

Sua means well, at least to a degree, suggesting Mizi can stay with her at zero cost. She may have ulterior motives driven by immense love and a desire for total codependence (which, again, makes me wonder of Sua's own past and how she could have gotten here albeit we have her ALNST counterpart to go off of), but she would obviously never wish to see her lover harmed. It's just that by housing her and by asking for nothing in return (and really, having Mizi beside her is enough), she can kill two birds with one stone. Not only will Mizi be safe, but Mizi will rely on her. Finally, Sua will be needed as much as she seems to need her. But what Mizi once again longs for in this world is a certain level of control to feel safe, whereas Sua wishes to be one with Mizi in a way that strips her of the very autonomy she craves. Ultimately, Mizi's needs win out over her own. Sua will prioritize her until the very end, if only in hopes that one day, the same devotion will be returned. If Mizi needs solace, she can find it in Sua. If Mizi needs to lash out, get angry, Sua can be on the other end of that, too. She won't mind.

Sua frames her "desire" for it as an attempt to finally understand her, but there's almost a sort of twisted thrill in it for her too, I think, to be who Mizi's attention is turned towards, whether for better or for worse. I think this is another means of Sua wishing to 'belong' to her, another way of insisting that Mizi is fully hers, too. An attempt to frame it all as romantic. It is also, of course, a way of Sua wishing to forget her own emotional pain that I'm sure she's feeling, replacing it with physical pain. While Sua says such things, she leans in for a kiss, distracting Mizi from both the harm she's brought to the rat and from the argument they're having, further supporting the fact that she has an incredibly unhealthy idea of what love is. It seems they once again have no plans to discuss the elephant in the room when it comes to how much they hurt each other both with words and actions, instead focusing as much as they can on this fantastical idea of their romance that isn't actually as soft or as pure as they try to pretend.

Mizi doesn't actually return any of it here. No slap, and no leaning in for the kiss herself, merely staring. She doesn't want to hurt her, as much as it's inevitable. She doesn't actually want to pretend everything is fine, either, to lose herself entirely in this idealized version of their relationship until the very end. She'll take the latter over the former, but it hurts her. It hurts them both.

No matter the universe, Mizi will always want to have just a bit of power, to have a choice. And it seems that just like in ALNST, in this world, that choice will be taken from her in the very end by the one she loves most. Just like how, in every universe, Sua would do anything but live without her.