Belief
The strongest thing in the world. It can give someone hope when everything seems lost and a feeling of power when you think that you can fight no more. Belief can make anything stronger, more alive and truer. From belief is how many religious gods got a name, how legends and stories are being formed.
It all starts with a name and one believer. The light spreads, from person to person and that name gains power. Slowly, it is more believed in and that name gets a form, then a face and then existence.
This is how the fairy tails came to be. How the protectors and the enemies of the children appeared and how they exist up until today. However, just like in every situation, there is a catch.
A small area that is not white or black but grey. There, no side can be taken, and no rules apply the same. In the case of fairy tales, you have the light side with the Guardians and the spirits; tasked to protect their children.
On the other side, you have the Boogieman and those who want to harm and terrorize the innocent bright souls of young children. And in the middle, in the grey zone, you have a single lonely figure with a task no one else wants, a task that makes them receive hatred and fear instead of admiration and love.
And that person carries it without a word of complaint. That person is Thanatos but nowadays, she goes by Grim Reaper...the Guardian of Life and the outcast of the Big Five.