Nina is an absolutely fascinating character. Like Victor, we struggle to understand just what she’s thinking. She’s married to Ferdinand, but carries on casual affairs with no thought to consequences. She doesn’t read her husband’s writing, but picks up enough from overheard conversations to quote it just the same.
A big part of Nina is her transience. As Victor says, she’s always either coming or going. He’s used to "her hesitations, second thoughts, third thoughts mirroring first ones, ephemeral worries between trains," and even imagines her as residing permanently in a train station, leaning over the counter, pondering a timetable. When he dreams about Nina, he sees her as a refugee in a train station. She even dies while in motion, traveling from one place to the next. Her presence in Victor’s life is always brief, intense, and forgotten immediately. She seems to offer her affection to anyone, willingly, completely, only to ignore them without feeling after the fact. What do you do with a woman like that?
The question is, what does Victor do with a woman like that? In his mind, in his memory, Victor has made Nina into something other than human. She seems to appear from nowhere, magically, like the bouquet of flowers in her hands at the end of the text. She defies time, appears "twenty at least" when she was seventeen, but looks far younger than her age at thirty-two. He sees her everywhere, even in magazines and fictional characters. He even characterizes her in series of set, fixed Nina-poses: leaning against a counter, sitting in the shape of a Z, holding a cigarette. She is always angular, slight, cavalier, at ease, and the focus of male attention. (Did you notice that men are always looking at Nina, starting with the Englishman whose blue eye draws Victor’s (and our) attention to her?) Of course, this is all rather unrealistic, and can only be the result of contrived artifice on the part of Victor. It’s unlikely that Nina lives forever in a series of angular poses, yet this is how she exists in "Spring in Fialta" because this is how she exists in Victor’s mind.
So, expectedly, we watch Nina break out of this cozy corner of Victor’s imagination. If he’s been treating her as an ideal, it is at the end of "Spring in Fialta" that the real Nina shows up. Unfortunately, the only way Nina can prove herself real is by dying. As it turns out, she’s not magic. She’s not immortal. She’s not a "salamander of fate" or an "invulnerable rogue;" she’s simply a woman who can die like anyone else. And that’s the real tragedy of "Spring in Fialta" – not that Nina died, but that Nina, as Victor imagined her, never existed in the first place.