Kill or Be Killed: Music as a Moral Catalyst in Toby Fox's Undertale

How Video Game Music Works

In Ludomusicology: Approaches to Video Game Music, Tim Summers defines ludomusicology as the connection between music and gameplay. However, defining music within the context of a video game is complex, as there is a lack of a musical score to support any conjecture concerning the music of the game. In order to establish any form of connection between music and gameplay, the gameplay itself must clarify that the music is different. Video game designers manipulate the game in a variety of ways; as described in Collins (2007), video game music falls into three categories:

1. Adaptive

2. Interactive

3. Dynamic

Adaptive video game music is the most fundamental element of video game design, as adaptive musical elements adjust to the order of narrative elements in a game. Interactive video game music is another critical aspect of game design, because interactive music reacts to the actions of the player in conjunction with the narrative of the game. Dynamic music, a combination of adaptive and interactive musical ideas, is the most difficult to artificially create; the game designer must anticipate how players will react to adaptive and interactive elements of the game in order to implement dynamic music.

These three categories illuminate the many roles that game music plays within the design of the game while also revealing the immersive qualities of video game music. Adaptive, interactive, and dynamic video game music are all player dependent, as the video game player must advance within the game world in order to activate specific melodies. This dependence allows music to take on a dual role that permits the music to both function as the ambiance of the game while also support the player’s understanding of the game’s next required action. By guiding the player to the next designed element of the game, video game music acquires a semantic identity. The music of a game gives elements of the game design cultural meaning within the context of the game, thus establishing the video game as a sort of simulation that invites increased levels of player self-awareness. At either the procedural or semantic level, video game music supports the player in understanding the game while strengthening player immersion.

Music Acts as an Ethical Stimulus

In a 2014 study, researchers Zhang and Gao ran experiments on levels of physiological excitement as demonstrated through increase in cortisol in combination with both violent and non-violent video games. Their results demonstrated that music in conjunction with violent video games saw a more dramatic increase in cortisol than in combination with non-violent games. The increase in cortisol in violent video games is logical considering that violent video games would have equally affective musical immersion that evokes predictable responses; dangerous or violent situations would have to be easily identified in order to maintain a level of player immersion. This confirms that there is a neurological response to video game music and the game environment that musical immersion creates.

Research on the autonomy of affect by Brian Massumi further illustrates the power of visual stimuli in relation to cognition. Massumi cites an experiment that administered mild electrical pulses to points on the skin and recorded when participants reported feeling the pulse; the cited results contend that there is a half-second temporal delay between affect and emotion when one is prompted by any category of affective stimuli. In the course of this half-second, higher processing functions are performed by neurological reactions occurring in the brain outside of the realm of our conscious understanding. The half-second delay prior to action and expression is understood to have a cognitive function that, through creating a temporal delay between affect and emotion, therefore plays a role in the formation of volition and response. Though perception occurs as an unconscious process, cognition is a conscious process that cements a series of associations that create a meaningful understanding of stimuli—what aurally fills this gap between perception and cognition has the potential to shape one’s understanding of the stimuli.

In order to establish and maintain player immersion, the music of a video game must guide the player to a series of actions that advances the plot line. If the game music leads the player to begin to kill innocent characters as an element of the plot line, the actions of the player must match the game fiction—this temporary suspension of morality both creates a different moral experience for the player and establishes a player’s ability to willfully suspend one's disbelief in order to continue the video game. This artificial moral experience prompts reflections upon one’s behavior outside of the context of the video game. When music in video games acts as a narratological or ludomusicological element, the music supports the player in broadening one's moral self-awareness, thus ethically influencing behavior both in-game and outside of the game.

Toby Fox's Undertale

Undertale was released by developer Toby Fox in September 2015. The game is a single-player, role-playing narrative adapted for PC, PlayStation 4, and PlayStation Vita. The player controls a genderless human child who must navigate through the Underground, a realm inhabited by monsters separated from Earth, in order to return to the surface. The player must interact with monsters through the combat system, which allows the player to choose to either pacify monsters or attack and eventually kill them. The game allows for three different endings, which are each dependent on how the player resolves encounters with monsters. The endings are commonly referred to as the Neutral Route, the Pacifist Route, and the Genocide Route.

The Neutral Route is the game’s default, and occurs if the player has chosen to kill some but not all monsters. In the first play-through of the game, the Neutral Route is the default. There are twelve variations of plot determined by which monsters are killed, but the Neutral Route generally ends with the human child fighting Asgore. Before the fight, the player is judged on the basis of how many monsters one has killed. During the battle, another monster, Flowey, kills Asgore, and the human awakens on the human side of the barrier.

The Pacifist Route may only occur after the player has completed one Neutral play-through. The Pacifist Route ending is generated by not killing any of the monsters while befriending two of the monsters, Papyrus and Undyne. When the player is required to fight Asgore, the befriended monsters intervene. As the battle goes on, Flowey ambushes the battle; using the befriended monsters as assistance, the player triumphs. The barrier between the human world and the Underground is destroyed, and the player is given the option to reintegrate with the monsters. The player is offered the possibility of accepting a monster as one's adoptive mother.

The Genocide Route may also only occur after the player has completed one Neutral play-through. The player generates this ending by killing all monsters that are encountered. The player is able to kill both Asgore and Flowey, after which the player is subsequently invited to partake in the destruction of the universe. To enable replays of the game, the human must give his or her soul to chaos in exchange for the restoration of the universe. Because the human child has given up his or her soul, the ending of every subsequent Pacifist route is marred by the presence of chaos. The presence of chaos is most clearly seen when the player immediately reboots the game after completing the Genocide Route (Example 1).

Perhaps the most striking element of the game is that a player must complete a Neutral Route in order to access either the Pacifist Route or the Genocide Route; in doing so, Fox creates an intentional juxtaposition of the Neutral Route and the subsequent play-throughs. This contextual comparison enforces Fox’s moral message that killing monsters has permanent consequences. Fox composed the music for Undertale with the intent of using leitmotifs that connect characters to new situations; however, this thematic interconnectivity of the music creates a platform that reinforces Fox’s own moral sentiments, especially when the music is modified from its original form in the Neutral Route. The first way that Fox reinforces morality is through the modification of speed. Anticipation is the 7th track that plays during any monster encounter while Toriel is with the protagonist. However, during the Genocide Route, the track plays at 0.25 speed when Flowey begins to grow afraid of the protagonist. This is especially significant, as the player original hears this track as contextualized and associated with Toriel, the game’s mother-like figure. This perversion of an otherwise positively connoted track casts an even darker contrast between the Neutral Route and the Genocide Route. Even more powerful is the final appearance of the track at 0.20 during the ‘The End’ screen of a Post-Genocide Pacifist play-through—that is, a player running the Pacifist route after completing a Genocide route. The semantic implication here is immense. Even though a player has most recently completed a run of the game without killing a single monster, the consequences of having completed a Genocide Route follow the player for the rest of the game (Example 2). Play-throughs that follow a completed Genocide Route are referred to as Soulless routes, and can only occur in the form of a Soulless Genocide Route or a Soulless Pacifist Route, as the Neutral Route remains unaffected.

Example 1: Screen Capture of player reboot of the game after completing the Genocide Route

Example 2: Screen Capture of the transformed ending of a Pacifist Route as impacted by a prior Genocide Route

Music as a Moral Catalyst in Undertale

Fox utilizes elements of adaptive, interactive, and dynamic music in order to discourage the player from choosing to needlessly harm otherwise innocent monsters. Fox modifies interactive music from the first Neutral Route of the game to convey the consequences of killing any character. By changing the interactive musical elements, Fox creates a dynamic musical experience that further immerses the player in the game while inundating the player with his moral message. I will show modifications to the Undertale soundtrack by placing the music of the original, Neutral Route alongside their modified counterparts in Audacity. There are two circumstances in which the music changes:

1) A Neutral Route track is modified during a Genocide Route

2) A Neutral Route track is referenced during a Pacifist Route

I will first address musical selections that are modified during the Genocide Route. In general, the soundtracks found exclusively in the Genocide Route are tracks from the Neutral Route that have been significantly slowed. The first example is a comparison of “Fallen Down” and “Empty House” (Example 3). “Fallen Down” is the fourth track, which plays when Toriel, the game’s mother figure, interacts with the protagonist. This track occurs at the same speed setting in the Neutral, Pacifist, and Genocide Routes, but, should the player decide to kill Toriel in the Genocide Route, the track that plays afterward, “Empty House,” is a slower version of “Fallen Down.” “Empty House” is 99% slower than “Fallen Down.” Fox reinforces the permanence of killing Toriel by programming the game to continue playing “Empty House” throughout the scene in Toriel’s home, regardless of the room the character enters.

This phenomenon may also be observed in instances involving the antagonist of the game, Flowey. Flowey is introduced in the third track, “Your Best Friend.” Though Flowey is not revealed as an antagonist until the final boss battle of each of the three routes, he is omnipresent throughout the gameplay. When the player reaches the maximum amount of kills for a certain stage of the game as one plays through the Genocide Route, the track “But Nobody Came” plays. When sped up 1300%, this track is exposed as a modified version of “Your Best Friend” (Example 4). By associating the track that plays when the player has killed every monster possible with the theme of perhaps the most evil character in the game, Fox implies that a player who kills all of the available monsters is not unlike the evil, twisted Flowey.

The Pacifist Route contains musical tracks that represent a synthesis of different motives from the Neutral Route in order to convey certain moral sentiments. A more prominent instance is “Fallen Down (Reprise),” which combines “Fallen Down” from the Neutral Route and “Once Upon a Time” (the first track in the soundtrack). The reprise plays when Toriel protects the protagonist during the final battle of the Pacifist Route—the connection to Toriel is recalled through the thematic material from “Fallen Down” while also expanding to connect the last battle of the game with the very first musical event as presented in “Once Upon a Time.” The fusion of the two songs reinforces the idea that Toriel, the mother-figure, is a benevolent omnipresence, and that her intervention in the final battle warrants compassion and gratitude from the protagonist. It is worth noting that Toriel does not intervene in the Genocide Route.

Fox also changes which tracks play during the Pacifist Route in order to highlight the permanence of ethically charged decisions. “Memory” and “Respite” both appear during the True Pacifist Route (as opposed to the Soulless Pacifist Route). “Memory” is the thirty-fourth track that plays during multiple critical moments in the game (e.g., when the protagonist begins to learn of Flowey’s evil nature, and when the protagonist saves Asriel), but sounds for the final time after the True Pacifist ending credits—the song does not play if the player has previously completed a Genocide Route. Fox deliberately omits this track from the Soulless Pacifist Ending, as “Memory” plays during scenes of the game in which the protagonist has heightened self-efficacy and increased awareness of others’ intentions. Similarly, “Respite” plays during the denouement of the True Pacifist Route. The track affirms that the player has made the morally correct choice by not killing any monsters, as the text on the screen reads, “This is the beginning of a bright new future. An era of peace between humans and monsters.”. “Respite” also does not play if the player has completed a Genocide Route.

Example 3: “Empty House” as a slower version of “Fallen Down” in a Genocide Route

Example 4: “But Nobody Came” sped up 1300%


The study of Toby Fox’s Undertale illuminates the potential for the use of video games as a platform that inspires moral self-awareness within players. Fox elicits a powerful form of self-awareness that calls for players to critically evaluate their behavior both within and outside of Undertale. Fox modifies the musical tracks through reductions in speed to admonish the player’s immoral decisions, and recalls positively-associated motivic ideas to praise the player’s morally sound choices. Though the music is changing in response to the player’s moral decisions, the game soundtrack retains its immersive qualities as the music of Undertale organically creates a balanced mix of adaptive, interactive, and dynamic musical elements. Additionally, video game music generally acts as a means to broaden self-awareness as the Zhang and Gao 2014 study revealed a physiological response to changes in music within the context of gameplay. Furthermore, the use of Audacity as a tool for analysis has enormous unexplored capacities, as it allows researchers to work with video game music within a virtual space. Ultimately, video game music works as an immersive agent that contains powerful capability to shape a player’s moral self-awareness which may lead to action in a player’s everyday life. Increased self-awareness as a result of playing video games has substantial potential to incite introspection and self-assessment of moral thought and behavior outside of the video game.


Collins, Karen. “An Introduction to the Participatory and Non-Linear Aspects of Video Games Audio.” In Essays on Sound and Vision, edited by Stan Hawkins and John Richardson, 263-298. Helsinki: Helsinki University Press, 2007.

Kamp, Michiel, Tim Summers, and Mark Sweeney. Ludomusicology: Approaches to Video Game Music. Sheffield: Equinox Publishing, 2016.

Massumi, Brian. “The Autonomy of Affect.” In Cultural Critique, no. 31 (1995): 83-109.

Munters, Gerald. “A Song of Good and Evil: Music as Ethical Stimulus in Video Games.” Dogmatix. W.T.S. Ideefiks, (Oct. 2016).

Undertale Wiki. “Musical Leitmotifs.” Last modified Jan. 29, 2018. wiki/Category:Music.

Zhang, Jiulin, Xuemei Gao. “Background Music Matters: Why Video Games Lead to Increased Aggressive Behavior.” Entertainment Computing 5, no. 2 (May 2014): 91-100.