Muir Castreia

A young Gabranth who thinks of Hiiro as an older brother.

~!Muir has awakened to her Binding, by exchanging a contract with the Spirit of Thunder.

In order to train to the level of holding her own as an adventurer, Muir, alongside Arnold, trained for six months under Rarashik!~

(Source: Konjiki no Word Master Wikia)