This Challenge is about Harry Potter and Pitch Black. There is slash between the two of them.
Also there should be a little Guardian bashing.
After Voldemort killed Harry in the final Battle Harry becomes the spirit of death.
When this happens he gets send back in time because the old spirit of death well died and there was no one suitable to take its place and to avoid a big mess with children being unable to move on the man in the moon send Harry to that moment.
(I hope you understand what I'm trying to say...)
His duty as a spirit of death is not to actually kill the children, but to guide them to the other side. Without him thy would be stuck as ghosts in the plain of the living.
While doing his job it is unavoidable, that he comes in contact with the spite of fear. And after some time they develop Feelings for each other.
Harry realises, that the fear of children is not necessary a bad thing, because it is there to protect them from harm.
Later, just before the dark age started something happened to Pitch, that mad him loos control.
Harry had been pregnant with their child, but they lost it and in blind rage Pitch went on a rampage.
Harry shared Pitch's pain and couldn't bring himself to interfere. He too grew cold.
Than the man in the moon send the guardians and Harry and Pitch where sealed away in separated prisons.
They didn't realise that what they had done wasn't the intention the man in the moon had had at all. He had wanted, that the guardians help Pitch and Harry to find there way again and not to endangers all children in sealing them away.
After Harry and Pitch were sealed away children were much more reckless and were often injured or killed because they didn't approach a situation with enough caution. And the spirits of the children had to find there way to the other side themselves.
Finally Pitch manages to escape his prison. In the time he was locked away he saw the error in his way and swore to himself, that he would find Harry and they would bring back the balance that was lost.
When he escaped he didn't start to spread fear anew, but he freed Harry and together they now had to convince the guardians of there sincere motives.
Where you put Jack Frost in all this is up to you.
Also Harry should get a guardian name and be called by that instead of Harry. The name itself is up to the writer.
I hope someone takes up my challenge : )
Ps: sorry for any mistakes in spelling or grammar...