OK. To Explain.
Fredd is chronically hyperactive. He can feel an emotionless form of anger and an emotionless version of joy. He works on pure impulse, he doesn't have emotional capacity to tell right from wrong. Despite being emotionally detached and sociopathic, he has a freak form of charisma. (Not real charisma, but enough enthusiasm to feign charisma.)
Felix is manically-depressed with suicidal tendencies. Unlike Fredrik, Felix does have emotional capacity. Though he has potential to feel a range of emotions, he is constantly spiralling deeper into depression. Though he is sensitive and caring (at point of overanalyzing) he has no interpersonal skills, and is misconstrued as being enotionless and uncaring.
I realised they are mirror images of each other in alot of ways and because of this, they'd have to be BEST FRIENDS!!! *insert sarcasm here*

By the way. This was originally drawn on brown natural paper with a sharpie marker and a bottle of White Out. =WIN