I will never tire of how the webnovel shows Navier falling in love.
One of my absolute favorite tropes in media is "What is this feeling?" - someone is experiencing an emotion or a set of emotions for the first time, and they don't know what's happening. It can be for anything, but most often in my experience, it's about falling in love.
The web novel does this absolutely beautifully, even from our duo's earliest interactions. Navier had once loved Sovieshu, but it was a subtle, quiet thing that built up over decades. Even then, it doesn't seem like she was ever more intimately attracted to him. That's in stark contrast to Heinrey, who took her breath away on first sight.
Gradually, we see her drawn in more and more: being mesmerized by his eyes, getting distracted by his physique, and having her heart set aflutter by some or his most sincere moments. She trusts him (more or less), and feels comfortable in his presence, but she doesn't seem to put together any of the pieces.
That continues after their reunion, but it has escalated. Navier finds herself touching his hands on instinct only to realize it and drop them, or feels "inexplicably" nervous but at the same time pleasant while around him, or gets flustered and distracted whenever she thinks about them bring a couple.
Despite us knowing what's happening as outside observers, Navier has never experienced this, and she has no clue what to do with it. It shows such a sweet side to the cool and competent Empress that I find so endearing. By the time she realizes she's physically attracted to Heinrey, she's already deeply romantically attracted to him, too, and that's both a novel concept and a terrifying one. But, she realizes she can't fight these feelings, and doesn't want to even if she could, and finally tells Heinrey she's in love with him. I love that whole journey.