Rain

Rhein (レイン), also known as Bleu (原初の青) is the blue Primordial and subordinate of fellow Primordial Guy Crimson. Guy was the one who gave Rhein her name.

Trivia

 * Her name has been said to originate from the English word "rain."
 * Rhein's name was changed between the Web Novel and the Light Novel version. In the Web Novel version, her name was Hirari instead.