"We're Worse Than You Thought"

This story is about a young girl, 16 to be exact who was born with a terrible problem, she had an alter ego and he was definitely not friendly, he was quite the opposite in fact, a complete opposite to the girl, he was loud, rude and evil, the girl However was quite soft spoken, sweet and an absolute angel, it would feel wrong to think ill of her when she's so nice to others but back onto the topic of her having an alter ego, this wasn't anything like she continued to the look the same she physically changes into a whole different person, her hair goes from a comforting brown to dark jet black, the warmth of her eyes leaving as she turned into a monster and this monster went by the name "Eli"

♤this is obviously a Jekyll and Hyde kind of story since that's my current obsession♤