Those who meet him eventually conclude, some more reluctantly than others, that Ayumu does have what it takes to 'save' the Blade Children, as they say Kiyotaka claims. As Ayumu investigates them, he meets five Blade Children Kousuke Asazuki, Rio Takeuchi, Eyes Rutherford, Ryoko Takamachi, and Kanone Hilbert, and is tested in various ways by them. They are distinguished by their cat-like eyes (though a few lack this feature) and by missing the seventh right rib bone. The Blade Children are the central mystery of the series, known only as cursed children that few know about and are being pursued by so-called Hunters. Together with his school's journalist, Hiyono Yuizaki, and the unwilling assistance of his sister-in-law, Madoka, Ayumu tries to figure out who the Blade Children are and what are their goals. Now in his freshman year of high school, Ayumu becomes involved in solving a series of murders, crimes, and other incidents, all related to the Blade Children. Ayumu's only clue as to his brother's whereabouts is the phrase 'Blade Children,' the only words Ayumu could make out in Kiyotaka's final phone call.

Plot Spiral: The Bonds of Reasoning Ībout two years ago, Ayumu Narumi's older brother Kiyotaka, a famous detective and pianist, mysteriously disappears without a trace. The series was also adapted as four light novels and a series of CD dramas. The anime is licensed in Region 1 by Funimation, who released it on DVD and broadcast it on the Funimation Channel, along with the programming block on Colours TV in 2006.

The series was adapted as a twenty-five episode anime television series broadcast on TV Tokyo from Octountil March 25, 2003. Yen Press acquired the license for Northern American release, and published the first volume in October 2007. Spiral: The Bonds of Reasoning was originally licensed for an English language release in North America by Tokyopop, however the company dropped the series. 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. 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. It was published by Enix and then Square Enix in Monthly Shōnen Gangan from 1999 to 2005 and collected in 15 bound volumes. Spiral: The Bonds of Reasoning ( Japanese: スパイラル〜推理の絆, Hepburn: Supairaru: Suiri no Kizuna) is a Japanese manga series written by Kyou Shirodaira and illustrated by Eita Mizuno.

Spiral suiri no kizuna ost