Looks like Mokou and Kaguya developed a different relationship than most authors depict. Competitive but not murderous, not loving but not hating. I like it, since it's a very different, and a much more complex take on their rivalry. They might still be trying to kill each other now and then, but their "fights" are mostly things like drinking games. Or at least that's what I take away from it.
So I got a song with the same name created for this story by another group.Just have a try guys,that's awesome (if you can get a translation of the iyrics)
In a way, their relationship is as "loving" as it gets here, both from Kaguya's perspective and Mokou's. As to whether it's a romantic or platonic kind of love, that's not really explored, but with both of them reflecting on how the other person is the one that makes them feel truly alive and both of them being the only people that can understand the other due to their condition (disregarding Eirin), there's certainly some kind of love involved. There's also Mokou's feeling about her first meeting which she called hatred before understanding it and now feels too frustrated to admit to, marked with a blush, so I don't think my yuri goggles are on too tight to say such an interpretation isn't too far-fetched. They're irreplaceable for each other, simply by virtue of what they are, both intrinsically and for each other.