Under

is a Japanese light novel series written by Kazuaki Sena, with illustrations by u. The series began publication on February 10, 2008 by ASCII Media Works under their Dengeki Bunko publishing imprint.

Synopsis
Midnight station. An unpopular coin locker. There, a girl was dragged into the darkness and disappeared. When a person dies, he falls into a “different world”. That is the rule of this world. However, the soul that has fallen into the "other world", leaving behind unskilledness, becomes a strange figure and returns to this world, causing erosion of the world. Yuito Kirisaki learned from a letter from his disappearing brother that there was an "otherworld messenger" who kept the balance of the world. The world of "darkness" that you meet while chasing the mystery of the whereabouts of your brother and the disappearance of the girl. Hunters and Things Hunted-What is the truth uncovered after a crazy feast? Psycho mystery colored by crimson sadness.