Names

At the beginning of Undertale, the player is given the choice of naming the fallen human.

Normally, the game asks "Is this name correct?" when asking for confirmation of the name, but some names trigger a unique response, and some of these names (mainly those of major characters in the story) cannot be used. Other names do not trigger any particular message but have a different impact on the gameplay. There is a six-character limit, but this can be bypassed using the renaming process as seen below.

Although this is depicted as the player naming the protagonist, it is, in fact, naming the first human to have fallen into the Underground. This name is mentioned by Flowey/Asriel, Asgore in the game over screen, the dream sequences in Toriel's house and Waterfall, the mirrors in Toriel's and Asgore's houses on a Genocide Route, the video recordings in the True Laboratory, and the first human's coffin. Notably, none of the characters ever speak the protagonist's name until they learn about it in the True Pacifist Route ending.

All names (except "Frisk") cannot be changed without performing a True Reset or completing a Genocide Route. Otherwise, when resetting, the message "A name has already been chosen" appears and the player is unable to change the name. "Frisk" is the only exception, as changing the name is required to leave Hard Mode.

Names with effect
Below are listed names that trigger something in the game. They are case-insensitive.

Forbidden

 * Alphys - "D-don't do that."
 * Asgore - "You cannot."
 * Asriel - "..."
 * Flowey - "I already CHOSE that name."
 * Sans - "nope."
 * Toriel - "I think you should think of your own name, my child."
 * Undyne - "Get your OWN name!"
 * Gaster - [Instantly reloads the intro sequence after flashing the confirmation prompt.]

Custom responses (Allowed)

 * Frisk - "Warning: This name will make your life hell. Proceed anyway?"
 * Murder or Mercy - "That's a little on-the-nose, isn't it...?"
 * Catty - "Bratty! Bratty! That's MY name!"
 * Bratty - "Like, OK I guess."
 * Temmie - "hOI!"
 * Aaron - "Is this name correct? ;)"
 * Woshua - "Clean name."
 * Chara - "The true name."
 * AAAAAA - "Not very creative...?"
 * Metta or Mett (Mettaton) - "OOOOH!!! ARE YOU PROMOTING MY BRAND?"
 * Jerry - "Jerry."
 * Papyru (Papyrus) - "I'LL ALLOW IT!!!!"
 * Alphy (Alphys) - "Uh.... OK?"
 * Napsta or Blooky (Napstablook) - "............ (They are powerless to stop you.)"
 * Bpants (Burgerpants) - "You are really scraping the bottom of the barrel."
 * Gerson - "Wah ha ha! Why not?"
 * Shyren - "...?"

Other effects

 * Drak or Gigi or Gugu - The Steak in the Shape of Mettaton's Face shows up as "FSteak" instead of "FaceSteak". This name is a reference to Gigidigi's Persona 4 comic, "Hiimdaisy". Notably, Gigidigi has also helped work on the game.
 * Frisk - In addition to having a custom response, this name activates Hard Mode.

Changing the name in the save files
Normally, the name cannot be changed except after a True Reset or giving your soul to Chara. However, it is possible to change the name during gameplay by modifying the game data.
 * 1) Go into "%LOCALAPPDATA%\UNDERTALE" on Windows (e.g. "C:\Users\YourName\AppData\Local\UNDERTALE") or "~/Library/Application Support/com.tobyfox.undertale/" on Mac.
 * 2) Open the file named "file0" with a text editor of choice.
 * 3) The name is stored on the first line. Replace it with a new name. Numbers and symbols can be added to this new name, but if it is longer than six characters, it covers surrounding text. Using a forbidden name has no effect.
 * 4) The name is also stored in undertale.ini and is displayed when loading a SAVE file, but it is be overwritten with the file0 name when the game is saved if they are different. If the game is reset instead of loading a SAVE, the undertale.ini name will overwrite the file0 name instead.

If the game detects that the name has been edited (for example, if it is longer than six characters), the text "Easy to change, huh?" appears in the stats menu. Oddly enough, this does not occur if a forbidden name is used.

Trivia

 * All forbidden names can be used in Undertale Demo.
 * Similar to above, entering the name "Toby" does nothing.

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