Imagine, you're a nature guardian charged with caring for a bear when, one day, the worst thing happens. A hunter comes into the woods.
You swear to stay with this hunter after that day. You'll remain with him, every second of every day, until his dying breath- and then you would take his soul as penance for your bear. Never allow this hunter to reach his mortal peace- because you surely won't find yours.
He knows you're there. Humans can sometimes feel your presence heavy and sometimes strangling, when it's dark. And once or twice he's seen you. For a long time this man ignored it.
Then he started talking to you now and then. You never spoke back. Not for years.
But it's amazing what you can get used to. Every animal he kills turns you more and more into something you were never supposed to be; a monster. Every little rabbit and every towering deer. No longer a peaceful nature spirit. A monster. And you're sad, and you're lonely. And you begin to talk back. Little whispers like wind or a bears claws scratching on bark. Only he can hear you.
You're becoming more and more a different creature. Your fingers have turned into gnarled black claws, your skin has turned sunken and a dark grey colour, your hair used to float around you- it now lays dead over your shoulders. You've grown horrifying stag horns that tower above you and look like terrible sharp, black tree branches. Your eyes are nothing but black holes. A bears fur creeps up your spine. You have a limp, because one of your feet is now a heavy moose hoof. The man can hear your steps. You don't have the strength to hide much, anymore.
You know you shouldn't leave him, you should get away. He's turning you into something horrible and wrong. But... you can't.
You whisper to him all the time. A lot of the time, you don't even hate him anymore. He's all you have; all there is for you.
Time goes on, many years pass; he's gone grey and he's gotten slow. You're not a spirit anymore. You don't know what you are.
... when he dies, you finally take penance for your bear. Take the hunters soul, bottle it up, never let him have peace. You also leave a kiss on his cold cheek.
This is an original Prompt! You're welcome to use it; If you do write something inspired by this please tag me so I can see!! <3