C³, also known as C Cube, is a Japanese light novel series written by Hazuki Minase and illustrated by Sasorigatame. The story revolves around a high school student named Haruaki Yachi, who receives a mysterious black cube from his father. The cube transforms into a girl named Fear, who is cursed due to her past as a weapon of torture. Together, they confront various challenges and threats linked to cursed tools and their dark histories.