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. His affection for Madoka (now as a "nee-chan") might also be because of formerly loving her, but stopped when Kiyotaka married Madoka. Ayumu is also the supposed only hope for the Blade Children and their survival.
In the manga, it is revealed that he is supposed to be a god to the Blade Children and that his fate is to kill the devil. It is also revealed that Ayumu is Kiyotaka's clone. 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 entirely useless. When Kiyotaka became a pianist, Mrs Narumi decided to create Ayumu to become a 'guinea pig'. If anything ever happened to Kiyotaka, Ayumu will 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. Hence, there was no more use for his clone Ayumu, and this is also the reason why Ayumu was often ignored by his parents.