I believe I've cracked the code on this one.
It can't be Sana, because she's a distant fragment. The kind of girl that you pass by occasionally and catch up with, something you two do ever since she helped you out that one time. But she's ephemeral. A fleeting memory. You don't want to be with her, you want to be with the memory of her. You will remember what she has done, and what she has accomplished, but not who she is. Faceless. She's the kind of woman that tugs at your neurons decades later as you stare down the shot glass, substituting her face for a squirming black squiggle. "I wonder what would have been," you think, "if I went for it." But you never did, and you never would have.
It can't be Baelz, because you lust for her. She breaks your back working for her but rewards you with a gentle kiss and a hug. Ultimately, she's an authority figure, a forbidden fruit that you can indulge in only if she allows you to. And then, even when she does, when she opens herself to you, you will realize: "I want to fuck this rat... But will I?" The reality dawns on you that all these fantasies of screwing your boss at the same shitty hole on the same shitty counter where you take shitty people's shitty orders might be better left as a fantasy. Your cock becomes flaccid, and she's disappointed. You never live it down. You work day after day, never able to look her in the eyes, never being ballsy enough to ask for a promotion as the years go by. One day, she retires. You do not.
It can't be Mumei, because you love her. Sure, she's adorable, and she's a retard, and she pulls at your heartstrings in all the right ways. On first encounters your dick and nipples go rock hard whenever you meet, every hanging syllable of every word of every sentence coming form her mouth indulging the mental scratch to your darkest itches. But then, one night, after the energy has calmed down, when you two sit there slightly buzzed, in comfortable silence, her voice comes out in a low whisper you've never heard before. And her insecurities and vulnerabilities and fears and wants come tumbling out unevenly, an uninterrupted waterfall of words as tears well up in her eyes. She grabs on to you, and you kiss. You never kiss her again.
It can't be Kronii, because she's simply too far out of your reach. Bullheaded, brash, and bantering, you two climb and climb, insteps and inclines, believing the world can be conquered. But time passes, and you slowly start to notice that the pathway you were striding on begins to diverge, and she seems to grow farther every single day. Regardless of your personal success, the sinking feeling of dread hits you as you understand your paths were simply meant to intersect, not follow. She grows farther and farther away, into the fog like a ghostly spirit. You reach out towards her in an attempt to clasp her, but she already has her back towards you, a twinkling star in the evening sky.
But Fauna? Fauna is the everyday girl doing her best. She's no splendid artist, nor trilingual world bridger, nor overnight sensation, nor wild child chasing her dreams. She's the down to earth girl that can kind of sing, that can kind of dance, that can kind of draw. The kind of talent that shines because she knows she's not a pure diamond and wants to show you everything of her. And you love her, because you see yourself in her, and what you can become as well. No, you two can't do things beyond your wildest imagination. But you can sing The Ink Spots with the ukelele under a tree as the midsummer afternoon light shines on you. You can take Bubba out for a walk, laughing at that silly old lady that always greets you while you're out. You can hold her hand, staring at the star-spangled sky because she woke you up at 2 AM and decided, "I can't sleep, let's go stargazing." The kind of girl you can grow old with, and learn with, and laugh with.