Well, I seem to have the advantage in terms of height and weight. Neptune is only 146 cm in height (about 4'9'') and weighs about 38 kilograms (about 84 pounds). I'm slightly more than a foot taller than her, and I may be a skinny guy, but I still weigh way more than that. This is, of course, neglecting the fact that she can wield broadswords that are about as big compared to her as the Buster Sword is to Cloud with the same proficiency as she can wield more reasonably-sized katanas with only some slowdown. Additionally, in the Neptunia games, she tends to be a glass cannon, though in the third game she was more well-rounded, aka the buffed all of her other stats to match her strength. This suggests that she has unnaturally high physical strength, even though she's about the size of an 11-year-old girl and spends most of her time lazing about and playing video games. This is probably due to the fact that she's a physical deity who has a mahou shoujo-style transformation sequence which lets her assume her goddess form, which is significantly bigger in every way. In this form, my height and weight advantages are significantly lower, since she's about 5'5'', which is still 5 inches shorter than me but is a lot taller than she used to be, and she weighs about 105 pounds, which is also a lot more reasonable since while I weigh a little more than that, it's only a few pounds. Additionally, she gets a sword that's even bigger than the aforementioned broadsword and the ability to fly.
So there are a few factors in play here, most of which are still going to let her kick my ass; it's just a question of how badly she's gonna kick my ass. Best case scenario, it turns out that her broadsword-wielding strength is just video game logic and this fight ends up being the laziest slap fight ever, with her getting distracted by pudding or video games or something halfway through. I'd probably win that, given that I could do that thing where I hold the top of her head at arm's length and then she can't reach me. If she actually does have super strength, then I might win under the aforementioned circumstances if I can outlast her. In a sword fight, I'd lose either way. In a 100%, all-in, serious fight, I'd lose so badly I probably wouldn't even exist any more at the end. And this is assuming I could even fight back against her. Wouldn't want to hurt her cute little face, after all.