Tobira no Soto

, is a Japanese light novel series written by Shinjiro Dobashi, with illustrations by Yukiko Horiguchi. The series began publication on February 10, 2007 by ASCII Media Works under their Dengeki Bunko publishing imprint.

The series won the Gold Prize in the 13th Dengeki Novel Prize.

Synopsis
When Noriyuki Chiba, a high school student who was supposed to go on a school trip, woke up, it was a closed room, and the whole class was locked up in the same place. An existence who calls himself "artificial intelligence Sophia" appears in front of the stunned party who does not understand the reason. The absolute “rules” shown to Sophia. However, Noriyuki refuses the asylum and curse from Sophia because of his momentary disgust. All the classmates except Noriyuki accepted the rule, and the strange daily life that the rule ruled began. Noriyuki, who was isolated, eventually made a decision ...