If you're not fairskin it's really difficult to find a character to cosplay so a lot of people were excited for her debut. She's a vocaloid from a computer program where you can create music, songs, and things of that nature. Here's some info about her character development and appearance concept from tumblr:
She is named after Merlinite (メルリナイト / Merurinaito) a type of stone known for its duel light and dark appearance.Her race’s concept as fairies is that they are a special race who can convert “songs” into “power”. They can only be seen by a subset of the human population. While Lapis’ power of song gives life, Merli’s draws energy from living things. Her official profile says, ”She’s 16cm fairy. She’s strong-minded and tsundere; she’s a charming mysterious girl, who is innocent and changing the facial expression all the time. She’s basically naive, but so innocent that she usually pretends to know everything ad hoc.“
source: Merli tumblr
