I find it confusing too, the most they share in common is just regular young stuff: arcades, close friendship, comfy living and trying fun dumb stuff. The most outstanding thing I can get is their shared martial arts. But rather than what they share in common, what they contrast in is a lot more interesting. From their opposite moles to their social status. On one hand we got the safe kid who wants to be less known for being safe and more like a rebel, while on the other hand we have the popular girl who's actually more of a rebel punk. That and also their roles as hero and villain, one wants to explore and be good while the other wants leave and do wrong. It's how they go about their world change as opposites that gives room for work, that and Sasha is a much bettet blonde than Star, that's a fact.