Barrier

For the music track of the same name, see Barrier (soundtrack).

(A strange light fills the room.)
(Twilight is shining through the barrier.)

Narrator, Asgore fight intro

The barrier (JP: バリア) is a strong magical force in Mount Ebott that separates the underground from the surface. It is located behind the Throne Room at New Home, and appears to be a silent, endless room transiting from white to black.

Beyond the barrier is a dark room with a sunlit patch of grass, and a purple arch depicting the Delta Rune. The barrier, as well as the patch of grass beyond, is only accessible on the Neutral Route and the True Pacifist Route.

Main story

After winning The War of Humans and Monsters, seven human magicians conjured the barrier with their SOUL power to protect humanity and keep monsters trapped in the underground.

Anything, including humans, can fall through the barrier and enter the underground's Ruins, where Toriel generally finds them. However, only a being with the SOULs of a human and a monster can pass through the barrier and exit the underground. The barrier can be broken, though it requires a huge amount of power equal to seven human SOULs, or six human SOULs and the SOULs of monsterkind.

Sometime after the fallen human's death, six other humans had fallen into the underground, and their SOULs were collected by Asgore. These SOULs were contained in glass vials, which had briefly been borrowed by Alphys for her experiments with determination.

Neutral Route

Asgore revealing the six human SOULs before his battle, with one container being empty.

When the protagonist crosses the arch with the Delta Rune, Asgore states that the following area is the barrier. He inquires if the protagonist has any unfinished tasks, and encourages them to take their time. Otherwise, Asgore summons the vials hidden in the room's floor and begins an encounter.

Following the battle, Flowey intervenes, absorbs the six human SOULs and becomes Omega Flowey. After the battle against Omega Flowey, the protagonist appears in the dark room with the sunlit grass outside the barrier, though the barrier remains.

True Pacifist Route

Entering the barrier is similar up to the battle with Asgore until Toriel and various monsters intervene. Flowey, after obtaining the six human SOULs, interrupts Toriel, saying that the protagonist should stay in the underground with him, and absorbs the SOULs of monsterkind to transform into his original self, Asriel. A battle against Asriel ensues.

After the protagonist defeats Asriel, he uses the SOULs of the six humans and monsterkind to break the barrier. It is depicted as being a near-opaque white with a large crack before splitting apart. Afterwards, the protagonist and most of the monster main characters appear outside of the gray Delta Rune arch.

Trivia

• On console versions of Undertale, the border is disabled in the Neutral Route at the barrier, as well as the room with the sunlit patch of grass beyond. On the True Pacifist Route, the border is enabled in the room with the sunlit patch of grass.
• Depending on the route, there is a slight difference when the protagonist nears and crosses the arch with the Delta Rune. However, the screen always fades to white once they cross through it.
  • On the Neutral Route, they cross through the arch without a prompt. After the white screen, it abruptly turns black, and the Undertale title and "By Toby Fox" appears. This is similar to when the protagonist goes through the arch with the Delta Rune at Home to enter Snowdin.
  • On the True Pacifist Route, the protagonist is briefly stopped by a message before being given a prompt whether to leave or not. After the white screen, it slowly fades in to a scene of the protagonist and their friends looking at the sunrise.
• The text after the barrier breaks lacks the typical dialogue sound bite, and the letters have additional spacing between them as the words are displayed at a slow pace.
  • The settings used for this text are the same used for the start of Asriel's phone call in the True Lab's elevator, as well as Sans's menacing tone during his introduction cutscene, MTT Resort date and his reminder about Papyrus's death at the end of the protagonist's judgment.
• The post barrier location resembles the Main Menu and two areas in the Ruins where Flowey appears. It is the area nearby the bed of golden flowers, and near the exit door of the Ruins, nearby Toriel's Home.