Board Thread:Legitimate Canon Questions/@comment-186.155.123.122-20140418035841/@comment-4091815-20140418125406

I could go into the angle of the wound, the fact that Derek was an Alpha, that Kali wasn't trying to kill him blah, blah, blah...

The fact is the writers wanted Aiden to die and so they had the Oni run him through vital organs - specifically his heart (although that was imperfectly presented on screen).

There is no canonical reason for why one died and the other did not.