What is BrotherFall?

Brotherfall is an Alternate Universe taking place after the events of the pacifist route Undertale. Frisk, as the ambassador of the Monsters is able to have lived peacefully for many unknown years. She, with the help of Alphys has been able to resurrect Chara and bring Asriel back from his form as Flowey.

Plot Summary

Frisk eventually has a child due to the wish of a dying friend whom she names the child after, Nathaniel. 15 years later, The brother of Asgore, long forgotten from the underground is rediscovered along with a legion of monsters at his command. Frisk attempts to make peace with them,with sans as protection, but ends up getting kidnapped and taken prisoner by Asgore's brother, Abbadon due to him still having a hatred for humanity and using the help of a revived Gaster to incapacitate sans. In order to save his mother, Nathaniel joins the army for the ensuing war. Eventually, sans awakens and reveals a plan to save Frisk by fusing the two's souls together, giving Nate sans's abilities, allowing sans to control Nate's body in certain times as the two now inhibit the same body, and effectively doubling their already tremendous power levels.

Nathaniel embarks on a quest, utilizing both sans's powers coupled with his military-grade weapons training in order to kill both Abbadon and Gaster in order to save his mom.

(The Story is still in Production)

Main Characters of BrotherFall


Sans is a secondary protagonist. Originally he was a wisecracking monster, and was the monster who purged the demon inside of Chara who incited Frisk's Genocide route. After Frisk gets taken away, he devises a plan to use the machine in his lab in order to fuse his soul with that of her son Nathaniel. He has become more silent and as such, leaves most of the talking and fighting to Nate.


Frisk is the mother of the main character, Nathaniel. She is kind and merciful and deeply loves her monster family. She has taken the role as the ambassador for the monsters of the Underground. She had Nathaniel at the request of a friend from before she fell into the Underground. Since he was dying, Alphys used his DNA which he provided through his blood to create the child. She is the new adopted daughter of Toriel and her current whereabouts are unknown.


Nathaniel is the main character of BrotherFall. Called "Nate" by family and friends, he has inherited the soul of determination and as such neither him nor Frisk have the ability to SAVE, LOAD, or RESET. However, he has put the determination to use in acquiring many of the skills that he would unknowingly need in the upcoming years. Before both the fusion and the military, Nathaniel is known to be skillful in fencing, and small bits of martial arts. He masters parkour just before the kidnapping of Frisk. In the military, with his now raging determination, he quickly ascends to become one of the most deadly soldiers, even after not having been in the military before. He becomes one of the most accurate soldiers in the force, able to use almost every weapon effectively. After the fusion, Nathaniel inherits all of sans's powers. He can summon bones, Gaster Blasters, and grab and throw souls. however, unlike sans, his fighting techniques are more unique, and he prefers surprise and aggressive attacks, attempting to quickly kill or force his enemy to submit with a sword made of bones. Nathaniel also uses his newfound weapons expertise in battle, using both bones and rifles at the same time. He also has the ability to use Gaster Blasters as well, but it hasnt been seen yet.


Abbadon is the main antagonist of BrotherFall. He appears almost identical to Asgore, but has a larger, darker beard. He wields a double-headed battleaxe as opposed to a trident. Abbadon has a deep hatred for humanity, and has raised a large army in order to crush the human race. Not much is known, but it seems he was abandoned as the monsters fled into the Underground.

Dr. W.D. Gaster

Gaster is a secondary antagonist of sorts. Not much is known, or seen of him. However, it is know that Gaster is the one monster that sans is afraid of. Enough so, that he has both froze up and ran away from him on two separate occasions. Once at the meeting of Abbadon, then after the fusion as Nate attacked Abbadon into submission. He is known to be a skeleton with the same powers as sans, but the ferocity of these powers is increased tenfold. he is known to be able to teleport by turning into a dark liquid, which he can also use for blending with water. This has not yet been seen.

Secondary Characters


Chara is the adopted child of Toriel and Asgore. She was killed long before Frisk entered the Underground, but was revived when Frisk fell. Her conscious remained inside Frisk for every RESET. During one of these, Chara was possessed by an unnamed demon, and took over Frisk's body. She then killed every monster in the Underground. Eventually, Frisk took back hold, and found a way to enter her soul and save Chara. sans volunteered to do this, originally with the intention of killing her, but when he discovered the presence of the demon, he killed it and Chara was revived. After the kidnapping and the fusion of sans and Nathaniel, she served as a trainer for a short time. Here, she defended herself as Nate made himself familiar with his attacks. For this, she used a short-sword, which glowed with determination. As of the story, her whereabouts are currently unknown.


Toriel is the mother of Asriel, and the adopted mother of Chara and Frisk. She also teaches at the local co-ed monster-student school, where Nathaniel was a student. She has a deep love for her children, and only a small understanding of who Abbadon is. Her whereabouts are currently unknown, but it is possible she is assisting in keeping the various children affected by the battles, safe.


Asgore is the father of Asriel, and the adopted father of Chara and Frisk. He has become the mayor of the state, and is normally very busy with his work. He does however, find time to spend with his family. Abbadon is his brother and he is uneasy when speaking about him. He is currently attempting to keep the peace with the civilians of the state.

Other Characters?

Most of the other characters have either been not written into the story or have not had large roles. These characters include:

Papyrus: Possibly later in the story, Currently in the prologue through the second chapter.

Undyne: Police officer/Security guard for Asgore

Alphys: Scientist, partly responsible for Chara's ressurection

Burgerpants: dont count on it.

Annoying Dog: ? maybe....He could either end up as a god, or just the skele-bros pets.

Leave questions in the comments below.

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