Fauna is one of three sister goddesses charged with countering the threat of Kousuke, a human unknowingly hosting a dormant devil's seed with catastrophic potential. Initially joining her sister Jordh to eliminate Kousuke preemptively, Fauna witnesses his inherent kindness, especially when he aids her. This compels her to spare him and seek another way to neutralize the demonic seed. She determines that extracting the evil seed requires repeated sexual acts, making this method central to her subsequent interactions with Kousuke.

Fauna, accompanied by Jordh and their younger sister, moves in with Kousuke to closely monitor and manage the seed. Their mission is complicated by Natsuki, an Underworld emissary posing as Kousuke's landlady, who actively works to ensure the devil awakens. Throughout this conflict, Fauna's actions are driven by her compassionate and protective instincts towards Kousuke. She operates within her divine responsibilities, balancing her duty to prevent global destruction with her empathy for him.