It is a tale from long ago
There was once a youkai child, specifically - amanojaku. That child was a curious one, it always strayed away from its family. And one of its beloved spots was near the human village.
It was very fascinated by human behaviour, which was very unlike the behaviour of youkai. It felt... Tender, close and loving. So it kept watching, longing, wishing to live their lives. To that child, it felt like their parents didn't give them enough attention, not enough... Love.
However one day, the child was noticed by a small boy - pretty much the child's age. The boy was also a curious sort, so he was fascinated by that child's horns and odd attitude - he didn't feel afraid of him. At first the child enjoyed his company, learning more and more about human emotions and feelings. However the more it hung out with the boy, the more jealous it became. Those emotions and feelings weren't alien to him while the child was struggling to wrap their head around; he is getting regularly fed and cleaned, something that is a luxury to that child; and most importantly, he lives in a commune - he has family, friends and relatives - those who love and care for him.
The child was a covetous child, and one day, during one of their secret plays, it flailed the skin, took off the clothes of the boy and left him hanging by the tree so it wouldn't run away, promising to give it all back once he gets to know his family.
It thought that if it pretends to be that boy, it would also be loved.
However, when the parents saw an inhuman child, wearing his bloodied clothes and his flailed skin of their beloved boy - they were enraged. The child narrowly escaped death and returned to the boy, giving back the clothes and skin which couldn't be returned. He accused the boy of lying saying "They hate you! When I came here, they immediately started yelling at me."
The boy was already crying out sheer agony of losing his face, but hearing that his parents hate him had disheartened him greatly. It couldn't speak, only sob and whine in pain - so the child left, not cutting the rope that tied the boy to a tree. It decided to go back to the den where it and his family resided, only to find it covered in blood and his family missing.
It couldn't understand what it was feeling at this moment. It couldn't grasp the gravity of the situation that the child found itself in. All it cared about is that it wanted to go to sleep.
And so, the child left that village and started observing another, hoping to fit into their commune and be loved. Soon, its disguises became more and more genuine. At first he would lure and kill the person he wanted to be in the shoes of; then adopt the quirks of said person and live out their life. Of course, there was only one flaw...
The child couldn't understand human emotions
No matter how much he tried, he couldn't grasp why people got angry at him, and so he had to change his identity quite often just to not get caught.
Eventually, the child would start to recognise certain patterns in human behaviour and even became able to grant people's darkest desires, but at the end of the day:
This covetous creature still doesn't understand emotions