User blog comment:Endless Exceptions/Champions Friends and Rivals list/@comment-8663856-20130512181240/@comment-6003864-20130513170014

I think RiotRunaan or Ransom (can't remember which) touched on this. Darius and Draven are brothers, and they'd die to protect eachother (Noxus is honor, not evil). But Draven is always overshadowed by he brother, and Darius likes being the strong one.