Pandora's Box (パンドラの箱, Pandora no Hako) is a box located in a room inside the Shibuya Mansion. The key given by Hitomi to Sakura can open the door to the room, and it is closely guarded by Inoichi, the mechanical doll.
Shibuya was shown to have extreme apprehension at the Code:Breakers entering the room because the room is supposed to hold the key to becoming the strongest power user. An example of someone who has unlocked this power is Toki. It can also be said that Haruto got his power from the box.
In chapter 180 it is revealed that on December 32, Sakura created Pandora's Box by sealing away the world-destroying Negation that occurred then.