C3 also known as C Cube, is a Japanese light novel series. The story begins with high-school student Yachi Haruaki receiving a mysterious super-heavy black cube from his overseas archaeologist father. That night, Haruaki wakes to a suspicious noise in the kitchen and discovers a stark-naked young girl with blue hair stealing rice crackers. The girl introduces herself as "Fear" (pronounced "Fia" in Japanese), and Haruaki comes to the conclusion that she is the cube that his father had sent. Fear explains that she is a Cursed Tool, objects which were used in the past by humans to fill out their evil desires. Over time they began to possess human attributes at a great price which include gaining human emotions, and hurting others without control. Haruaki assures her that he is immune to any curse that she might give him, and vows to help out by getting rid of her curse. Allied with next-door neighbour Konoha Muramasa and the strict class representative Kirika Ueno, they try to help her remove her curse, but in the process gets involved in many dangerous organisations, and other Cursed Tool incidents.