I find her sexy not because of her appearance, but because of a certain personality I perceive about her.
S/M features the most expressive characters we've seen in the Pokémon series with some of the most developed interpersonal stories, and yet Chicken-chan stands out among them as someone who remains stoic and forward despite everything happening around her.
Even though she's a young, fledgling Trainer, she's very mature for her age and and charges forward on her journey, taking what she wants when she wants it with pure confidence. That does wonders for fantasizing, because it allows me to imagine a confident Chicken-chan getting what she wants rather than someone taking advantage of her.
And I think many of the artists think the same way, because more often than not she's shown with a confident smile or a sly expression, even if she's taking it from a man. It's especially apparent when paired with a meek character like Lillie, where Chicken-chan is usually the dominant one rather than the other way around. Hell, I've seen her portrayed as dominant even when paired with characters much older than she is.
Basically, she has this sexually adventurous and confident aura about her despite being so young and seemingly innocent, and it's a fulfilling dichotomy to indulge in.
