Nobuyuki

Description
Nobuyuki is the protaganist of Zetsubou Prison. He wakes up in a locked room, seeing a sign saying 'Welcome to Zetsubou Prison', and from there Nekohiko and Kyodo task him with hunting down the doppelgangers, in return for his memories. For this he enrols in Kaigokoro Academy and joins the occult club. Because he does not remember his name, he introduces himself as Nobuyuki.

In his middle school years he transferred to a new school, where a boy named Masaki and his friends were the first to be friendly to him. He had fun as part of their group for a while, but a school trip to Kyoto would ultimately lead their friendship to break. Seeing a ceremony at a shrine, where papers with wishes written on them were burned, Masaki's group decides to try it themselves, in a cave near their school.

Nobuyuki objects, and ultimately waits outside while the others perform the ceremony. When he hears screams he rushes in and calls for help, but ultimately two of the boys die - and what's more, in questioning, Masaki blames it on him. It is from this despair that Nobuyuki's doppelganger was born.

His real name is Kousei Aida.