The only way to open the door was if the players who authenticated had their numbered bracelets added up to 26, which could also be seen as a "9" in base-10 or "q" in base-27. In the case of the game, 2 + 4 + 5 + 7 + 8 = 26.
A misconception is that all it takes to open is a digital root of 8, which is untrue. For example, if Junpei, Clover and Lotus used their bracelets (5 + 4 + 8 = 17 = 1 + 7 = 8), they would not be able to open it. This door does not use digital roots.
Behind Door q
The DEAD is right behind the door. A large, spiral staircase can be seen up ahead, behind a silver door. The staircase leads up to the top deck of the ship on the Gigantic. In Building Q's case, it's the exit and leads to the roof.
- In the Japanese version of the game, the explanation for why the door opened was that the letter "q" and 9 make the exact same sound in Japanese (kyu).
- For this reason, in the English version Zero never says "Seek a door that carries a ." through the loudspeaker, but in a written note that is not present in the Japanese version.
- 9 is an unlucky number in Japan and 苦 (ku) can be translated as "pain, ill, suffering, agony, torture". As such, 9 holds a widespread superstition in Japan. This is likely why the final door is located in an incinerator.
- In the First Nonary Game, this door actually was a 9. This is seen in the flashback of the game and was the only thing that was changed for the Second Nonary Game. Snake also states this door opened for a digital root of 9 during the First Nonary Game.
- Ace, in some of the bad endings where he is able to freely escape, would likely have trouble working through Door q and may have had to use trial and error.
- In the Axe Ending, is is implied Clover does not escape past Door q. It is possible she is incinerated to death in this ending because she lacks the bracelets.
- It is unknown if the 3 - 5 bracelet rule still applies to Door q.
- In Virtue's Last Reward, the final puzzle room is a highly complex room known as Q, its name referring to the quantum mechanics (namely Schrödinger's Cat) that are used in that room. Noticing its name, Tenmyouji says "Really? Now someone's just being a smartass."