Rumpelstilzchen

"Oh, how good it is that no one knows that I..." With these words, the little runt dances around the fire, thinking that no one is listening to him.
For he once helped the poor miller's daughter to spin straw into gold and now he wants her first-born child as tribute. To prevent this, she has to guess his name. But what is his name?

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Image source: Kurenai