Door 2 is one of three choices in the third set of numbered doors the Nonary Game participants find themselves faced with, the other two being Door 1 and Door 6. Unlike the previous sets of numbered doors, these doors are not on the same deck as one another, let alone in the same room.
Door 2 is on the Bottom Deck of the ship after going through the Mercury Elevators. It is found by Junpei and June. It leads to the confinement room and then to the torture room. Choosing Door 2 will always lead to the Sub Ending.
If the player chose Door 3 earlier, they are forced into Door 2 (except in the iOS version where Door 3 leads to the Syringe Ending). Going through this door will always lead to the Submarine Ending, regardless of which door you previously took.
Previously through Door 3 (excluding iOS version)
With only the Mercury Keycard in hand, the group of seven know where they need to go next. They activate the elevator and take it down together to the Bottom Deck, where they find Door 2.
Knowing now that all the doors will eventually lead them all back together until they find Door 9, the group decide to send only three people in.
Previously through Door 7 or 8
The group, having found the next three doors on three separate decks, decide to do a sort of voting. Each person writes down the numbered door they wish to enter on a piece of paper, and after everyone had, the results are read out one by one. This is to ensure no one can just suddenly change their decision to enter the doors for whatever reason.
The result of the voting is as follows:
Junpei, however, has a trick up his sleeve. He had prepared three pieces of paper, one for each of the three doors. Door 6 was placed on the ground by default, but he had Door 2's in one of his hands. After reading where everyone else wants to go, he decides to take Door 2.
Choosing Door 2 partners Junpei with Seven and Lotus.
5+7+8 = 20 = 2+0 = 2
This leaves Ace (1), Santa (3), Clover (4), and June (6), whose digital roots are incompatible together for another door. However, Clover suggests that Ace, Santa, and June go through Door 1.
1+3+6 = 10 = 1+0 = 1
Clover volunteers to stay behind, as she wants to be left alone anyway.
Behind Door 2
The DEAD of Door 2 is found just beside the door, on the other side. Beyond Door 2 was the escape room itself, which consisted of a small hallway that branched left and right, lined with old, rusty doors. A quick look around reveals that they found the confinement rooms.