Casey Callow, a prestigious member of the Protection Guild, has her sights set on understanding the rare power over darkness plaguing her country of Calgonia. In a land where everyone possesses an ability over either water, air, earth, or fire, darkness stands out as a dangerous and mysterious fifth element. But darkness is not the only thing plaguing the country. Rival to her own guild, the Assassin Guild poses threats to Calgonia with their less than moral undertakings. After the estate of the esteemed Onendilo family is ravaged by darkness, Casey soon discovers the Assassin Guild is more sinister than she once believed. She finds herself partnered with the enigmatic ex-Assassin, Noriko Ondendilo, as she works to uncover the truth of the Assassin Guild and its connection to darkness. Through trials of trust, love, and humanity, Casey and Noriko strive to save those closest to them from falling into the clutches of the Assassin Guild. Can the duo uncover the plot of the Assassins in time? Or will the Assassins' use of darkness consume all they know to be true?