Complex sentence: Due to their same appearances, Nami ties her hair in pigtails, but her hair is slightly longer than Sora's when let down, the only noticeable physical difference aside their gender.
Split into simpler sentences: Due to their similar appearance, Nami ties her hair in pigtails. Her hair is slightly longer than Sora's when let down and this is the only noticeable physical difference between them aside from their gender.