Spiral: The Bonds of Reasoning is a Japanese manga series written by Kyo Shirodaira and illustrated by Eita Mizuno. It was published by Enix and then Square Enix in Monthly Shōnen Gangan from 1999 to 2005 and collected in 15 bound volumes. The series focuses on Ayumu Narumi and his efforts to solve the mystery of the Blade Children, cursed geniuses with cat-like eyes lacking a seventh rib bone. A prequel series by Shirodaira and Mizuno, called Spiral: Alive, was published in Gangan Wing and Monthly Shōnen Gangan from April 2004 to June 2008 and collected in five bound volumes.

Gangan is a manga imprint owned by Square Enix Holdings. It originated as a manga imprint for Enix before the company re-branded as Square Enix. It publishes manga in several anthologies aimed at different reader demographic groups in the Japanese market. Its anthologies are home to some popular Square Enix manga series which were adapted into anime series, like Fullmetal Alchemist, Moribito: Guardian of the Spirit, Nabari no Ou, Inu x Boku SS, The Case Study of Vanitas and Soul Eater. The comics are later collected in paperback volumes under brand names such as Gangan Comics , Gangan Comics Joker and Young Gangan Comics , which identify the anthology of serialisation. These paperback brand names are formed by omitting any gekkan or shōnen in the magazine name and inserting Comics directly after the word Gangan.