Aizawa, Kouichi

Rokujo's 14-year-old classmate who studies nindō under Kumohira. Though he normally has an energetic attitude when around others, he is serious and relentless when it comes to his ninja duties, and is apparently fascinated with death.

[Spoiler] It is later revealed that his love of death is a result of his own inability to die. His immortality is attributed to the holder of the Shinrabanshō during the Edo Period, who was a medical practitioner, experimenting with placing the wisdom of the Shinrabanshō into animals, since humans usually died. There were only two survivors of the experiments, both of whom gained immortality as a result. Kōichi's ultimate goal is to find a way to die, as well as ensure that "monsters [like himself] are never created again." [/Spoiler]

He was born on July 31.

[Spoiler] At the end of the manga, he and Shijima disappear along with the Shinrabanshou, their immortality having been lifted. [/Spoiler]