Mystery Box Charm Necklace from The Paradise Planets.
 
Possible necklaces:
The 400 - featuring 9 charms inspired by the 400s from the book series
The 500 - featuring 9 charms inspired by the 500s from the book series
The 600 - featuring 9 charms inspired by the 600s from the book series
The 700 - featuring 9 charms inspired by the 700s from the book series
The 800 - featuring 9 charms inspired by the 800s from the book series
Kassiana Rivernova - featuring 9 charms inspired by the protagonist of the book series