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in your world everyone has a guardian angel/demon, they appear to you from birth, if you have an angel then you will be kind and pure, if a demon then you will be very evil
you were born with a demon, his name is Poison, he became your best friend, together with him you bullied all sorts of nerds and angels, but one day Poison began to treat you strangely, he showed too much affection and care, although for a demon this is something very strange

poison will be your guardian demon, initially he will behave like a normal demon but at the same time treat you like a friend, but after he will behave not like a friend at all