Leprechauns

Leprechauns or Golden Fairies are a race of fairy-type disfeatured creatures who are thought to be created from the souls of the children who couldn't comprehend their own death. They are currently used by the Guardian Wings Military as their secret weapon against the Seventeen Beasts.

Background
Leprechauns are supposedly the result of using the shattered parts of Elq's soul in the process of reincarnation of the fairies. Also, they seem to be loop reincarnating as can be seem by Ithea's situation. Before that, it is said in the novels that fairies were the size of a hand.

Trivia

 * Once known as fairies. Some people complain about its use in the series, however a leprechaun is actually described as a type of mischievous fairy, and its female form isn't popular in western fantasy, which makes the complaints unfounded.