Spiral: Bonds of Reasoning(2000)

Spiral: Suiri no Kizuna

"I'M GOING TO UNCOVER THE MYSTERY OF THE 'BLADE CHILDREN.'"

World-class detective Kiyotaka Narumi's last words prior to his sudden disappearance continue to haunt his younger brother, Ayumu. The cheeky 10th-grader becomes further embroiled in the mystery when he is mistaken for the prime suspect in a murder at his school. Led by Ayumu's sister-in-law, Kiyotaka's wife and fellow detective, Madoka, the investigation into the murder gives Ayumu a chance to clear his name. But in doing so, he not only uncovers ties to the Blade Children but also more questions than answers about who and what they are.

(Source: Yen Press)