Dia is just what the younger form of her and Nol's species looks like
- So Nol and Dia are siblings, but look like different species, with Nol looking like a bipedal cat and Dia being a rabbit-like Waddling Head. Assuming it's not a case of Bizarre Sexual Dimorphism or (one of) them being adopted, maybe Dia just hasn't grown into the "adult" form yet? All we know is Dia is younger than Nol, and they share traits like pointed black tails and body markings on their ears, face and limbs. Maybe as Dia grows older, her body will grow to look more like Nol, with her face shifting upwards and turning into a separate head and her "ears" shown to actually be arms (note the similar markings on her ears and Nol's paws). She may or may not already have cat-like ears hidden by her bow.
