Undertale Heart Guide

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Undertale was one of the first games to truly transcend the barrier (no pun intended) between simple graphics and narrative depth within the modern wave of pixel-art indie games.

We learned the simple joy of returning to an art form of the past with titles like Minecraft and Super Meat Boy, but Undertale showed us how thought-provoking worlds and poignant stories had their place in this new-old industry pivot.

The game’s ability to create a heartwarming (or horrifying) tale and a believable world out of what is a basic, even considered ugly, aesthetic is one of the main reasons it remains so popular today.

Hedging my bets on the other main reason for its proliferation across the gaming landscape and beyond, I’d say it was its surprisingly deep and complex lore.

The hidden context and further reading Toby Fox created for Undertale have kept fans speculating and theorizing today, and the way he drip-feeds tantalizing information through this game and his other project, Deltarune, serves to keep fans hooked on the greatest secrets.

Whether it’s Halo or The Lord of the Rings, every well-fleshed-out backstory has to start somewhere. In Undertale’s case, it all begins with the concept of souls and hearts.

Having played through the game countless times and read reams of information covering context, I’ve written this article to provide you with a fundamental understanding of the core of Undertale’s world.

We’ll discuss the history of the monster and human worlds, how hearts function, their significance within the plot, and some extra information I found along the way.

Souls and hearts are similar concepts. While this article will focus mostly on contextual story elements, we have another article—Undertale Souls Guide—to get you up to speed on the main gameplay elements of Souls. With that out of the way, let’s investigate this often confusing yet engaging topic!

Bottom Line Up Front

Like many of our Undertale lore articles, this piece is pretty in-depth. If you don’t have time to read everything, here’s what I would consider the key take-home information.

  • Hearts are essentially the physical manifestation of the soul.
  • They come in several colors, with each color representing certain attributes: bravery, perseverance, determination, kindness, patience, and integrity.
  • Monster hearts are upturned and colored white.
  • Seven human souls are required to break the barrier in the underworld and free the monster population.

Spoiler warning: Naturally, there will be many spoilers ahead. I only recommend reading on if you have finished Undertale at least once. Preferably, it would be best if you played through it three times to get all three possible endings, as I will be discussing elements of each.

Some Background: the History of Monsters and Humans

the war of humans and monsters undertale

The War

From playing the game for the first time, we understand that Undertale is underpinned by a previous and unresolved bloody conflict between humans and monsters. This battle was aptly named “The War of Humans and Monsters,” and it was the monsters that suffered a heavy defeat.

At one time, humans and monsters coexisted and ruled the earth together. We still don’t know why the war was started, but we do know that humans attacked first. They were intrinsically fearful of their only weakness as a species: that a monster could absorb a human soul, making them inexorably powerful.

In their normal state, however, the monsters’ strength as a group paled in comparison to the humans’. Even if all the souls of each monster citizen were combined, the power would still equal that of only one human.

Because of this great disparity, the humans decimated the monster population without a single human casualty—not one human soul was taken, even though this was the initial fear prompting the attack.

The humans reigned victoriously, and gathering seven of their most magically talented, they sealed the remaining monster population beneath Mount Ebbot and conjured a barrier so that they would never escape.

Deep beneath the mountain, the monsters created a new home for themselves. Naturally, they wholly blamed humans for the war. Their leader, Asgore, declared war on them and vowed to kill any human who stumbled into the underworld.

Their souls would then be harvested in an attempt to obtain seven, the number required to break the magical barrier and allow monsters to travel to the surface.

As such, souls are at the heart of the very essence of Undertale’s story of war and conflict, but what are they exactly? And what do they have to do with hearts?

What are Hearts?

Hearts and souls are essentially the same thing; the heart is used to depict a soul, and many different colors denote separate attributes. Within Undertale, there are seven colored hearts in total. Their attributes are as follows:

  • RedDetermination 
  • OrangeBravery 
  • YellowJustice 
  • GreenKindness 
  • PurplePerseverance
  • Light bluepatience
  • Dark blueIntegrity

These seven heart colors represent a myriad of different concepts, with their virtuous definitions coming to represent many of the game’s main characters and even the general themes seen throughout the story.

Unlike monsters, a human’s soul does not correspond to their essence. Instead, it is a component of them that is housed within a physical body.

A monster’s soul doesn’t have any color. They are depicted as white and upside down, and they’re considered the very essence of a monster’s being. This difference in makeup is one of the main reasons that humans are so much more powerful than monsters in terms of their physical prowess.

All human souls also represent the special quality of “determination,” an attribute that enables human souls to persist after death. Before we move on to each of the fallen humans, it’s important to briefly discuss this innate quality.


hearts undertale

As with many concepts in Undertale, the idea of determination breaks the fourth wall. I briefly described above that determination is an intrinsic attribute of human souls; it essentially enables them to exist after death.

Because a monster’s very being is interlaced with its soul, once they die, that’s it; they return to dust. For humans, only their physical bodies are destroyed when they die.

In the game, the most determined being in the underworld can save As you may expect, this being is us (Frisk), meaning that we never truly give up.

Because we possess determination, we can continually return to the game as many times as we like, even if we fail over and over, thanks to our determination, which allows us to save the game. You’ll have noticed that whenever you save, a quote is displayed denoting why, at that moment, you are particularly determined.

Can a Monster Possess Determination?

Yes. It may not be expressed as strongly in humans, but it can exist in monsters. It may even exist in small amounts in all monsters.

One monster that we know exists in unusually high amounts is Undyne. If you decide to kill Undyne, you’ll notice that she refuses to give up right until the bitter end. Eventually, her body begins to melt.

While you may have thought this was just added for a particularly gruesome end, this is a physical manifestation of a monster acquiring too much determination.

Alphys’ Experimentation

Most of the in-game information we learn about determination as a substrate comes from the True Pacifist route. On this route, we can explore Alphys’ lab and discover the experiments she’s been doing with its energy.

Alphy built a device called the DT Extraction Machine, which she used to physically extract determination. She would then inject the substance into fallen monsters in the hope of reviving them, but this didn’t work.

Instead, the injected monsters became a revolting mass of flesh and sinew known as Amalgamates; they remember nothing of their past lives and have deteriorated to a much lower form of sentience.

Aside from the amalgamates, Alphys also performed an experiment on one of the golden flowers found in the ruins. This wouldn’t have the same effect as creating an amalgamate, but it would result in a much worse creation: Flowey.

Flowey gained sentience because, as long as a thing possesses determination, it can also develop the will to live, even if it doesn’t have a soul.

At the end of the neutral route, we see all colored hearts harnessed under the power of PhotoShop Flowey, and it’s here that we learn the most about them.

The Seven Fallen Humans

the seven fallen humans undertale

The seven colors and their ascribed virtues are fundamentally tied to the seven fallen humans, each of whom fell down into the Underworld from Mount Ebott and died at the end of their journey.

During the game’s final act, when the player is about to meet Asgore for the first time, they can carry on past Asgore’s chamber and down a flight of stairs. This room presents an eerie array of seven coffins, each with one of the colored hearts inscribed on the surface.

Each coffin represents one of the seven fallen humans, and throughout the game, we learn the secrets of who they were. Frisk’s own coffin, denoted by his red-colored heart, lay open, waiting for him.

As you may expect, each human is thought to have possessed the virtue associated with their color, but exactly how or why has been left up to player interpretation.

During the final fight of the neutral route with PhotoShop Flowey, we momentarily fight and then enlist the souls of the other six humans to help us.

Each of these fights is unique, with imagery and attack patterns that hold relevance to the fallen human’s past life. Upon stealing the hearts, Flowey had hoped to become the most powerful being that ever lived, but this power trip is denied when the souls resist and help the player instead. Let’s explore each of the fallen humans now:

Red: Determination 

Red is the most unique color of all souls, as it represents both Frisk and Chara. However, many fans have come to question the reliability of the red color marking the virtue of determination.

Considering that Alphys’ research dictates that determination is a core quality of all humans, many think that the red heart represents something else. What that is, exactly, has many interpretations. I found this thread on Reddit particularly interesting (the community discusses the philosophy underpinning the attributes of the red heart).

Orange: Bravery 

The brave soul attacks using outwardly spinning gloves with a symbol on the back of the hand and heals using another set of hands with their thumbs up.

In Snowden, the player can purchase an item named “Tough Glove” for 500 gold from the Bunny Monster’s store. Given the above, this item is believed to have been in the position of this particular fallen human.

Due to the ethereal nature of this fallen character’s associated items, it has been difficult for the community to form theories about what happened to them. The most common theory seems to suggest that the character stood up to Sans and lost.

Yellow: Justice 

yellow justice undertale

The Justice soul fires at the player with a large revolver and heals us with four-leaf clovers.

A cowboy hat and a revolver can be purchased from Bratty and Catty in their store in the alleyway next to MTT Resort. These items carry the pretty obvious connotation that this human was a cowboy of sorts, perhaps a sheriff. Given this assumption, we could also suppose he or she is an adult human and not a child.

The fact that the gun was empty when found suggests shots had been fired, and there’s one theory that proposes the yellow soul died at the hands of Undyne: that she’s missing one eye because she was shot.

Green: Kindness 

The kind soul attacks us with frying pans, healing with cooked eggs. In Hotland, we can find a frying pan and a stained apron. There are a few aspects to note here regarding the green human’s lost items.

Firstly, we know Triel cooks. Perhaps both the frying pan and apron are from a previous interaction with her; maybe she took them in as she did Frisk.

Of course, this would only explain why the character possessed these items. Another theory suggests the character both acquired the items from and died at the hands of Mettaton. After all, we know Mettaton hosts a cooking show and even tried to kill Frisk while he stared at it.

Purple: Perseverance

The perseverance soul attacks us using fast-moving on-screen text with scornful definitions and heals us using positively charged words.

Also found in Waterfall are the possessions of the Perseverance soul. Speaking to Gersund and inspecting the items for sale, we can purchase cloudy glasses and a torn notebook. These items likely hint at this human’s proclivity for reading and writing.

Unfortunately, we can’t read the notebook. When we try, the words within are described as illegible, but they would no doubt have provided key information about their life and possible death.

Light Blue: Patience

The patient soul attacks us with an array of spinning daggers and heals us with bandages. In a room in The Ruins, the player can find a toy dagger that is presumed to be associated with the light-blue fallen human.

One of the most interesting theories I’ve found relating to this character came from another Reddit thread. Here, the original poster convincingly argues that the patience human is actually Suzy, a relatively rare character that only spawns sometimes in Undertale and has a larger role in Deltarune.

The entire theory would be too much to delve into here, but Suzy is thought to have a deeper connection with Frisk due to the dialogue spoken by Clamgirl, the significance of the item she carries, and a strange photo that hangs on the wall of Sans’s lab.

Dark Blue: Integrity

undertale soul colors

The integrity soul attacks us with a flurry of stars and oscillating ballet shoes, healing us with musical notes. It” can be assuredly assumed that this character was a dancer, and hidden behind a waterfall in Waterfall, we can find an item named ‘Old Tutu.”

A lot of fans consider that the Integrity Soul may have been quite violent. The Old Tutu is covered in dust, and anyone who’s played Undertale even for half an hour knows that monsters deteriorate into dust the minute they’re killed.

Given their love for dancing, we may assume this human was fit and agile; perhaps they managed to combat and defeat some of the slower monsters.

Breaking the Barrier

As I briefly mentioned earlier, the hearts and the way they operate have a fundamental hold on the denizens of the Underworld. Asgore has killed and will kill each and every human to fall to the Underworld since Chara and considers doing so a necessary evil for freeing his people.

Alongside the coffins we see laid out beneath his chambers, we also see the physical manifestations of souls as hearts when we fight him during the neutral route.

Before the battle ensues, Asgore can be seen with each soul he has already captured within a transparent mason jar, and there’s just one empty one left for Frisk. As we know, seven souls are required to break the barrier, but this isn’t the only way one can do so.

As an extreme, though theoretically possible alternative, the barrier can also be broken with six human souls and the souls of the combined monster population.

The barrier has only been broken once, and it ended in tragedy. Again, you can read more about it in our Undertale Characters Guide, but Chara and Asriel’s joint efforts allowed them to reach the surface together through the sacrifice of Chara’s soul, which was then absorbed by Asriel.

Some Interesting Theories about the Colored Hearts

In this last section, I’d like to come across some of the more interesting theories I’ve come across regarding this topic. Undertale lives on through this sort of discussion, so let us look at some of the more pervasive theories that have been pondered over the years.

The Heart and Soul Descriptions Represent the Virtues Required to Spare each Boss

undertale the heart and soul descriptions

I’d considered this idea myself after I finished my first True Pacifist run, and a year or so later, I found a post by u/Astery91 that fleshed it out.

Consider that to spare each of Undertale’s main bosses, you must display the virtue associated with one of the colored hearts. In this theory, each boss has its own relevant virtue the player must display:

Papyrus: Integrity: Despite his bravado, Papyrus is a wholly innocent character. His only objective is to be appreciated, and even if you lose to him, he will never kill you. Because of this, the player requires integrity to not mercilessly kill Papyrus.

Muffet: Perseverance: Muffet is considered one of the more grueling battles in the game. Her attacks are plentiful and versatile, and every now and again you have to fight a sort of mini-boss in the form of a monster cupcake. Considering this, you need perseverance to make it to the end and spare Muffet.

Toriel/Asgore/Flowey: Determination: To spare each of these three characters, you need to continually press the spare button, ignoring the character’s unacceptance. In this sense, you are determined to accomplish this task.

Undyne: Kindness: More so than most other characters, Undyne is merciless in her attempts to kill you. She presents as one of the more fierce characters in the game, and she’ll stop at nothing until she hunts you down and does what she feels is the righteous deed. Considering her unwavering lust for your blood, to display her kindness and spare her is the ultimate selfless act.

Alphys: Justice: This is a slightly more abstract one, but Justice is considered to be at play when the player confronts Alphys about her actions. As we learn, Alphys was involved in some highly questionable experiments involving human souls, even going so far as to inadvertently create Flowey in the process. This isn’t to mention all the fallen monsters that turned into Almagamates at her hands. Many players believe Alphy’s actions to be wholly reprehensible, and so to choose to challenge her on them displays justice.

“Frisk is a Combination of Determination and Justice

It is commonly suggested that Frisk’s red heart, representing determination, is a combination of all characters, but the following theory goes a step further than that.

If we take a look at the combined colors of yellow and purple, they create red, perhaps indicating that Frisk’s character is a combination of these two traits in particular. Interestingly, this idea scales across all moral decisions in the game.

No matter how you choose to play or which path you pick, perseverance is a virtue not just in Undertale but in virtually any game. Frisk never falters on his journey throughout the underworld, and few would deny he is perseverant above all else.

Then we have justice, an idea that has no absolute grounding in the forces of the universe or human nature and is instead determined by the person’s own thoughts and ideas.

Whether Frisk chooses to spare or kill a player could be considered a manifestation of their own personal definition of justice, and as such, it applies to Genocide, Neutral, or True Pacifist runs.

Considering the other colors or virtues, it would be much more difficult to argue against this theory. Kindness is obviously out, as Frisk has the potential to be unwaveringly cruel, while killing every monster you come across is neither brave nor patient.

There are More than Seven Colors

soul colors undertale

While we only see seven colors manifest themselves in the game, many fans have considered that there are likely a whole lot more colors that describe the nuance between them.

With this theory, the hues are viewed more as on a spectrum than as absolutes; combining different colors together can make different hues, resulting in traits that are between two colors.

I particularly like the depiction in the image below. Here we see a total of twenty-two different traits, and together, the whole thing covers a broad spectrum of different colors.

Out of all the theories I’ve seen, this one has the most fundamental grounding in common sense. Segmenting a person into six distinct traits allows for none of the variability we associate with the complexity of one’s personality.

A depiction of the possible spectrum of other personality traits as depicted by hearts RP Undertale RP

Frequently Asked Questions

Question: Were all the Fallen Human Children?

Answer: This question is one of many unsolved and likely unsolvable mysteries about the game. Given the implication that Toriel remains in the ruins to care for each fallen human, as well as the juvenile nature with which she is implied to care for them, it has often been assumed that the humans that fell were all children.
However, this has never been confirmed. It is entirely possible that some of the other humans were adults, and as far as I can tell, there’s nothing to disprove this theory.
While Toriel’s depiction would suggest the other fallen humans may have been children, her reaction to Frisk may be out of a longing for her own child, Asriel. Her actions do not necessarily mean she behaved the same as every other human. So, this is one you’ll have to make up your own mind on!

Question: Will we ever Discover Exactly what Happened to the Fallen Humans?

Answer: Given Toby Fox’s love for cryptic messages, I consider it highly unlikely that he’ll reveal the answers to what happened to the fallen humans outright. That doesn’t mean that we won’t get more information through subsequent games, however.
As is the case with all of Undertale and Deltarune’s mysteries, Toby Fox loves to drip-feed information and have the player search the depths of each game for clues. Of course, that’s one of the main reasons we’ve come to love his games so much and why they’ve stood the test of time.

Question: Why are Frisk and Chara’s Soul Colors the Same?

Answer: As briefly mentioned above, Frisk and Chara share the same colors. red as their soul —The relationship between Frisk and Chara is an incredibly complex one—something far outside the scope of this article – but in its simplest denotation, the color is a metaphor for these two characters being two sides of the same coin.
As is depicted most blatantly during the genocide route, Chara’s soul inhabits Frisk’s body in some capacity; we see this when her dialogue is displayed when rummaging through Toriel’s house at the end of the game on this type of run.


I hope you enjoyed this article on Hearts and Souls and, most importantly, that it provided you with a greater understanding of the world of Undertale. For more information on the game’s plot and lore, check out the Undertale board on Reddit.

This is the best place for discussing theories and ideas with the community. I’d also suggest checking out the smaller but always interesting Undertale Theories subreddit for more interesting takes. Have fun! 

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