Spoiler warning!
This section contains plot details about the novels.

Deadlock Among Mirrors was a world created by Yukito Tejima with his wish to create "a world containing only him and his ideal girl." However, when he used the box, he did not believe his wish would really come true, trapping him in a mirror maze filled with oversized, lifeless dolls of the girl he loved, Suzu Amemiya. In volume 7, Maria Otonashi was trapped inside of his world for a year (equivalent to one day in the outside world), and after convincing Tejima to give up the box, destroys it.