Sora

Sora (ソラ), a fairy from the Fairy Tribe, was given the job of protecting the forest and safeguarding the Shield Of Truth. She gave the shield to Rein and others after they told her it is needed to defeat the demon lord. Noticing that she is sad, Rein asks her to tell the reason. Sora told Rein and others that his sister was captured by Shadow Knight as an offering to protect their village. Rein helped her and her sister by defeating Shadow Knight. Then, Sora, along with Luna, decided to join his party, making them his third and fourth contractual.

She's one of the main heroines of Beast Tamer series.