Inked: She got Rowling’s writing tattooed on one arm. Demon Slayer has become one of the most popular anime series since its debut last year. Her most prized possession, though, batman costume is a letter sent to her by J.K. Something special: Her most prized possession is a letter sent to her by J.K. And they found these books, and they found out that the Dementors were actually written to represent depression.