Main Characters (Spiral: The Bonds of Reasoning)

Ayumu Narumi (鳴海歩 Narumi Ayumu?)
The protagonist of Spiral, Ayumu is very intelligent, but is very introverted and has a lot of self-doubt. He fears that he cannot surpass his own perfect older brother and doubts himself to the point where he no longer believes he can do anything anymore without acting like his brother. He is a talented pianist like Kiyotaka, an excellent cook, and cares a lot for his sister-in-law Madoka. In the manga, he tells Kirie that he was going to switch his type of woman to "Looks aside, someone who I can rely on, even when I am an inconvenience to others. It seems like I need such a girl," implying Hiyono. Ayumu is also the supposed only hope for the Blade Children and their survival.
He is revealed to be a clone of his brother. In fact, he and Hizumi are the first clones to be made, and thus have a very limited life span with many biological complications. Ayumu was created as an 'insurance' for Kiyotaka by his parents. Mrs Narumi was also a pianist before she suffered an accident, resulting in the loss of function of her fingers. She tried numerous chemicals and treatments to regain the use of her fingers, which eventually led to her fingers becoming almost entirely useless. When Kiyotaka became a pianist, Mrs Narumi decided to create Ayumu to become a 'guinea pig'. If anything should ever happened to Kiyotaka, Ayumu would first undergo treatment to find out whether it was suitable for Kiyotaka's body system. However, at his last concert, Kiyotaka publicly announced that he would give up the piano to become a detective and crushed his fingers on the piano. His mother saw no more use for his clone Ayumu who was often ignored by his parents after that.
In the end, he is hospitalized because of his biological complications. Having lost the use of his left arm, he continues to write music, still adhering to his way of fighting destiny: to live on, creating new opportunities and generating hope under his own power. This is the answer he gives to the Blade Children.
Voiced by: Kenichi Suzumura (Japanese), Daniel Katsük (English)

Kiyotaka Narumi (鳴海清隆 Narumi Kiyotaka?)
Ayumu's older brother, who is perfect at everything in the eyes of Ayumu. He became a world-class pianist after the age of ten and then an unimaginable world-class detective at twenty. He married Madoka - but left a year after they married. He is also the real reason why Ayumu always doubts himself, who is constantly comparing himself to him. Kiyotaka left one day after he was researching the mysterious case of the Blade Children. Many assume he is now dead. Ayumu discovers that he is not, after hearing that he has been associated with the Blade Children.
The anime never offers an explanation of his disappearance. In the manga, he is revealed to be the puppeteer behind the scenes, and returns at the very end. He created a situation where Ayumu would lose every last bit of his support, even Hiyono, but Ayumu managed to overcome despair on his own. He lives with Madoka and still controls his organization from Japan.

Hiyono Yuizaki (結崎ひよの Yuizaki Hiyono?)
The infamous school journalist, Hiyono is the bubbly and energetic sidekick of Ayumu, always stuck to his side. Very clever and a quick-thinker, her confidence borders dangerously on overconfidence. She is extroverted and is Ayumu's polar opposite, serving as one of the series' few comic-relief characters. Her skill with computers are as amazing as her hacking abilities and she has access to over one hundred resources. She blackmails Wataya often, and is very fond of Ayumu's cooking (to the point where she even thinks along with Rio that she wants to become his bride). Hiyono is also one of the few who whole-heartedly believe in Ayumu; she also has a great deal of faith and loyalty in him, and is also hinted by Madoka and herself that she has some feelings for Ayumu.
At the end, it is revealed that Hiyono was also part of Kiyotaka's machinations. The reason she knew so much about individual Blade Children, such as Kanone's foster parents' names, is because Kiyotaka told her. She is in fact older than Ayumu (ironically the type of girl he likes), and being "Hiyono Yuizaki" was just an assignment. She was to be Kiyotaka's final trump card—Kiyotaka would reveal her identity to knock away Ayumu's support.
After the final confrontation between Kiyotaka and his clone Ayumu, "Hiyono" left for her next assignment in Germany, for two years. The manga ends with an epilogue where Hiyono is visiting Ayumu in the hospital. Ayumu's left arm was paralyzed due to the complication and he is seen playing the piano one last time in the series with Hiyono listening.
At the end of the anime however, the camera view shows a field of purple iris and the viewers can hear Hiyono and Ayumu exchange a few words. Apparently they are on a picnic and Hiyono has packed them lunch. Ayumu takes a bite of her food but doesn't appear to like it very much, ending with Hiyono complaining to him.
Voiced by: Masumi Asano (Japanese), Caitlin Glass (English)

Madoka Narumi (鳴海まどか Narumi Madoka?)
Ayumu's sister-in-law and Kiyotaka's wife, she works as a police detective but is usually outsmarted by Ayumu in most cases. Her investigation skills are remarkable, but because of work she is rarely at home and therefore can do no domestic work. She cares a great deal for Ayumu. She is pretty selfish, not quite aware of the pain her brother-in-law endures because of how much he cares for her since she is his only family now that Kiyotaka has gone missing. Madoka tries to keep Ayumu from getting too involved with the Blade Children, but proves to be another weak spot of Ayumu and is often left in the dark by Ayumu about situations concerning the Blade Children for her own safety.
She lives with Kiyotaka and visits Ayumu in the hospital. Spiral: Alive reveals her maiden name to be Haneoka.
Voiced by: Kotono Mitsuishi (Japanese), Gwendolyn Lau (English)

Suemaru Wataya (和田谷末丸 Wataya Suemaru?)
A detective in training, he works under Madoka and isn't very smart as he jumps to conclusions without thinking about a situation thoroughly. He is regularly blackmailed by Hiyono and often hangs out with Madoka in a bar.
Voiced by: Bin Shimada (Japanese), Robert McCollum (English)