Okay, so to have a better idea of what I'm going for I'll pitch the specific character I'm wanting to make with the harbinger.
Upon reaching puberty however, it became clear that his curse was more than skin deep. Slowly his family realized the boy himself was a conduit for abyssal malice and fury far greater than himself. His mere presence inspired conflict and at times he would play host to it himself.
Life at the manor became increasingly tense until the now teenage demonmarked killed his uncle who had taken it upon himself to drown the young man. Fleeing in exile, he took to the life of a wanderer. Getting by largely on his relatively expansive education and reluctantly harnessing his demonic power when knowledge proved insufficient. An unusual sight at the dives he frequents, the road worn and weary traveler, absent of bravado and with a saddlebag full of books rather than treasures.
Initially he would be restrained and concerned with keeping a low profile. Struggling to come to terms with his existence.
Upon his return at level 6, he would be rather more comfortable with himself. Not seeking out danger but unconcerned with avoiding it. Trouble would find him regardless, it always did.
That's where I'd like to take this character, it's up to you to decide if it and the harbinger class would be a good fit.
Thinking about it though, it's possible that the character could also work as a Bloodrager if you're not sold on the path of war stuff.
Just let me know what you think when you have time. I'm in no rush so long as the recruitment will be continuing for a bit :)