No. 6 is a series of nine novels written by Atsuko Asano. They were published by Kodansha from October 2011 to June 2011. The novels are the foundation for the manga adaption (March 2011) and the anime adaption (July 2011).
The story takes place in an ideal city known as "No. 6". Shion, a boy raised in the elite and privileged environment of his home, gives shelter to another boy, who only gives his name as 'Nezumi', during the former's 12th birthday. After spending a rainy night with his new friend, Shion discovers the next morning that Nezumi has left and disappeared without a trace. Four years later, Shion experiences a spate of incidents around him in which a deadly infection by parasitic wasps leads its victims to age rapidly. Shion's co-worker is one of the victims and Shion is arrested on suspicion of murder. Whilst Shion is being transported to the Correctional Institute, Nezumi appears and rescues him. Shion begins to find out the hidden truth behind the Ideal City No.6.