Eight Humans

The fallen Eight Humans are the only humans from the surface who have fallen into the Underground through Mount Ebott.

They include the First Human, the six human Souls that Asgore has collected, and the protagonist. Each Soul Mode and colored Attack Type correspond to one of the Eight Humans.

History
Prior to the events of the game, seven humans have fallen into the Underground.

The first human to fall was Chara, who was found and then befriended by Asriel. Later Chara was adopted by Toriel and Asgore as a second child. At first, things seemed bright for the underground. The human and Asriel became close. One day, though, Chara became very ill. Before they died, their last request was to see the Golden Flowers from their old village.

During the Pacifist Run, it is revealed in the True Lab that Chara had poisoned themself so Asriel could absorb their soul and go to the surface to get the six more human souls needed to break the barrier. Asriel absorbed their soul, and crossed the barrier carrying Chara's body to a field of Golden Flowers near their old village to fulfill their request. The human inhabitants of the village saw Chara's body and misunderstood, thinking that Asriel had killed the child. They attacked and mortally wounded Asriel, who didn't fight back and returned peacfully to the Underground. Asriel then turned into dust in the throne room, in the spot where the golden flowers would then start to bloom in the Underground for the first time.

The shock of this tragedy caused an enraged Asgore to declare that all humans who fall into the Underground will be killed and have their souls collected for the purpose of permanently destroying the barrier, afterwards waging war on humanity.

The reasons for Chara's travel to Mount Ebott are uncertain, but in the end of the True Pacifist Route, Asriel says he believes Chara left because of their hatred of humans, and that Chara didn't always have the best intentions.

Sometime after then and before the start of the game, six additional humans traveled to Mount Ebott and fell into the Underground; each with their own associated items, each for their own mysterious reasons. Every one of these six humans was killed, and their souls were stored for use by Asgore. Their bodies were kept in coffins near Asgore's throne room.

Main Story
The protagonist is the Eighth Human to fall. Their decisions and Determination shape the Underground, the timelines, and the entire world.

Neutral Route
Before initiating combat in Waterfall, Undyne tells the player that six humans have had their souls taken from them, and that the player's soul will be the seventh and final one required to break the Barrier.

Later at the barrier, Asgore reveals the six souls he possesses right before attacking the player. After he is defeated,  Flowey  absorbs the souls to become a powerful creature, Omega Flowey.

During the fight against Omega Flowey, the six souls and their items are used to attack the player one at a time. If the player calls for help through the ACT option offered in battle ('You called for help...'), the soul will assist the player by using green attacks which heal them. After receiving help from all six souls, they reduce Flowey's defense to 0 and regularly send green attacks to the player. After he is defeated, Flowey loads the game to a SAVE file when he was at full health, but the souls revolt again, removing his abilities and leaving him helpless to the player.

Sans tells the player after the credits that the souls have disappeared, precluding the plan of breaking the barrier through their use.

Genocide Route
Near the Genocide Route's end, Alphys and Flowey both urge Asgore to absorb the six souls.

In the very end, Chara themselves appears in person to speak with the Player, having fully possessed Frisk by now. You can try to stop Chara, or go along with their plans, but no matter what the player does at this point, they will destroy the world and its data, crashing the game, ending the Genocide Route, and permanently changing the Player's SAVE file.

Upon launching the game again, the Player only sees a black void. After ten minutes, Chara will appear and offer to recreate the world—in exchange for the Player's Soul. Refusing will force the Player to wait another ten minutes. Accepting will allow the player to RESTART the game, but with permanent corruption of the True Pacifist Ending.

True Pacifist Route
Toriel points out that Asgore could have absorbed a single soul to cross the barrier and find six more humans to collect the souls of if he really wanted to break the barrier, similar to Asriel and Chara's original plan.

Flowey steals the six souls and absorbs the monsters' souls to regain his form as Asriel. He then turns into his ultra form, and fights the protagonist while mistaking them for the first human. The protagonist saves Asriel, after saving all of their friends, who accepts that the first human is gone and learns that the eighth human's name is Frisk. Asriel releases the souls after destroying the barrier, allowing Frisk and the monsters to leave the Underground. If you travel to the beginning of the ruins, you can find Asriel in his child form sitting in the golden flower bed.

The seven coffins near Asgore's throne room are opened, either to prepare the humans' bodies for burial or indicating that the humans had been restored to life with the return of their souls. The first human's coffin is empty, as Toriel buried their body in the Ruins when she moved there.

List of Human Souls
Further information: Soul Modes

The following is a list of human soul colors of the Seven Humans and details associated with these colors.

Red Soul

 * Trait: Determination
 * Associated Items:
 * The Eighth Human (Frisk):
 * (Beginning of Route) Stick and Bandage, the items that the Player starts with.
 * (End of Route) Worn Dagger and Heart Locket in Asgore's Home.
 * The First Human (Chara):
 * (Genocide Route) Real Knife and The Locket in Asgore's Home.
 * Combat Mechanics:
 * Normal Mode: Free movement. Sprouts legs when running away.
 * Snowball Game Text: Try as you might, you continue to be yourself.
 * Owners: The first human, Chara, and the eighth human, Frisk.

Aqua Soul

 * Trait: Patience
 * Associated Items: Toy Knife and Faded Ribbon found in the Ruins.
 * Combat Mechanics:
 * Light-Blue Attacks: Inflicts damage unless you do not move.
 * Photoshop Flowey: Attacks with Spinning Blades. Heals with Bandages.
 * Snowball Game Text: "Ball" is "Small". You waited, still, for this opportunity... then dethroned "Ball" with a sharp attack.

Orange Soul

 * Trait: Bravery
 * Associated Items: Tough Glove and Manly Bandanna from Snowdin Shopkeeper.
 * Combat Mechanics:
 * Orange Attacks: Inflicts damage unless you move through them.
 * Photoshop Flowey: Attacks with Spinning Gloves with Eyes. Heals with Thumbs Up.
 * Snowball Game Text: You are the kind of person who rushes fists-first through all obstacles.

Blue Soul

 * Trait: Integrity
 * Associated Items: Ballet Shoes and Old Tutu in Waterfall.
 * Combat Mechanics:
 * Jump Mode: Jumping over foes and objects.
 * Photoshop Flowey: Attacks with Ballet Shoes and Stars. Heals with Music Notes.
 * Snowball Game Text: Hopping and twirling, your original style got you through.

Purple Soul

 * Trait: Perseverance
 * Associated Items: Torn Notebook and Cloudy Glasses from Gerson.
 * Combat Mechanics:
 * Trap Mode: Moving along Muffet's spiderweb.
 * Karmic Retribution: Inflicts Sans' Karmic Retribution (KR) poison damage.
 * Photoshop Flowey: Attacks with Books and Negative Words. Heals with Positive Words.
 * Snowball Game Text: Even when you felt trapped, you took notes and achieved the end of "Ball".

Green Soul

 * Trait: Kindness
 * Associated Items: Burnt Pan and Stained Apron from Hotland.
 * Combat Mechanics:
 * Shield Mode: Standing still and shielding from Undyne’s spears.
 * Green Attacks: Heals you.
 * Photoshop Flowey: Attacks with Frying Pans and Fire. Heals with Eggs.
 * Snowball Game Text: Your care and concern for "Ball" brought you a delicious victory. (Kindness)

Yellow Soul



 * Trait: Justice
 * Associated Items: Empty Gun and Cowboy Hat from Bratty and Catty.
 * Combat Mechanics:
 * Shooter Mode: Heart is upside down and shoots bullets upwards toward foe.
 * Photoshop Flowey: Attacks with a Loaded Gun. Heals with Four-Leaf Clovers.
 * Snowball Game Text: Your sure-fire accuracy put an end to the mayhem of "Ball".

Trivia

 * Because the ability to LOAD and SAVE the game is associated with Determination, and Determination in turn is associated with red souls, it can be surmised that none of the humans other than Frisk and the first human had the ability to LOAD out of their demise.
 * While not directly stated, it can be assumed that all of the humans that had fallen down into the Underground had been of a young age, although the highest and lowest cannot be determined.
 * Hints to this include the reference Toriel makes when talking about how "each human that falls down here ends up being killed once they leave" and how she's seen it "time and time again."
 * This, coupled with the large box of children's shoes that can be found in your bedroom, and the child-like nature of most of the items that have been connected with said humans, all point towards the idea that the Six Children that appeared between Chara and Frisk were in fact of a younger, more child-like age.
 * When playing the Ball Game, the player may achieve any of seven flag colours, all of which have a different message and each of which correspond with one of the heart colours (Red, Orange, Yellow, Green, Light Blue, Dark Blue, Purple.)Nzo72CF.png
 * If you achieve the red flag, You will also get descriptive words, each highlighted in a colour that seems to correspond with each heart, other than red, which is the player's heart colour.
 * The descriptive word in red, "Determination", appears instead at each save point during genocide runs.