Warning - Rant incoming.

Ayumu has a brilliant mind but his older brother Kiyotaka was even more incredible leading Ayumu to be introverted and self doubting, this gets worst when Kiyotaka goes missing when he investigated the Blade Children.
But when murders start happening around Ayumu relating to the Blade Children, Ayumu becomes intent on solving the mystery behind Kiyotaka and the Blade Children aided by enigmatic reporter Hiyono, but the Blade Children are keen to test Ayumu to see if he really is the one to save them.
I'm going to just say it, this is the worst anime of the 00s. How I judge bad is dependent on a few factors, and Spiral falls under, competent anime trying way too hard. The problem is, the Blade Children are shown to be twisted freaks of nature who aren't afraid to murder just to hide their secret but the way they challenge Ayumu breaks one of the fundamental rules of mystery thrillers which is the payoff. Spiral fails at this by making it clear way too early that Kiyotaka is pulling the strings, hardly a spoiler as it's made obvious as early as the first 7 episodes that he is, so they resort to an insulting twist near the end that ruins any integrity the story had left. What makes it worst is that Ayumu frequently lampshades the fact that the Blade Children are trying way too hard to challenge him to these games of death when a handgun could do the job much quicker.
It's a pity really as it started so well and it is impressive how Ayumu gets round some of the challenges but it's undermined by the fact that his brother is an ass hole for setting all this up, I feel sorry for Madoka.
Dub is fine, Ayumu and Hiyono were the best of an otherwise regular bunch of voice talents.
Final Verdict: A poorly written mystery that insults the viewer the more it goes on.