The story follows Merla, daughter of the former governor of District 20. After giving up her entire inheritance, Merla joins the Public Defense Force to help protect their home from the beasts that always lurk. Her home being one safe haven of many where Arc Crystals protect the people from Miasmic Beasts.

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As these attacks surge in frequency, Merla finds herself alone. She feels as if she is the only one who sees the chaos that is about to befall them. With tenuous new bonds, she must find a way to curb the destruction of districts across the region.