Lust

Biodata

Background / History

Lust’s Underground suffered from infertility following the queen’s miscarriage. After the king killed a fallen human who had abused monsters, Dr. Gaster extracted the lust trait from its soul and injected every adult monster—including himself—with it. The treatment failed to resolve the infertility and instead intensified desire throughout the Underground, with members of the Royal Guard becoming especially brutal 41.

Lust was the first to recognize the injected trait’s danger. He approached Alphys and Gaster about removing it, but both had become dependent on it and were more interested in satisfying their desires. As the trait threatened his own sanity, Lust built a portable suppressor. It preserved his self-control, but could neither eliminate the trait nor be mass-produced with his available materials 42.

To protect Papyrus from monsters who tried to assault him, Lust dragged the attackers into Gaster’s hidden soul-storage maze and killed them. The lust within them revived them as increasingly mutated creatures. During later research visits, Lust discovered that his suppressor concealed him from their lust-based senses; after a close encounter, he stopped returning 45 48.

Although Lust had worked for the Royal Academy of Sciences, Gaster and the others excluded him from experiments involving the Determination Extractor. He remained unaware of both the machine and the concealed True Lab until his counterparts showed him 43 48.

Appearance

• Long hair: Keeps a comb and brushes his hair while recounting his world’s history 41.
• Pink eyes: His eyes glimmer pink when discussing the Royal Guard’s corruption 41 42.
• Revealing clothing: Dresses provocatively like the surrounding monsters, but the narration identifies this as an attempt to fit in rather than an expression of comparable desire 41.

Personality

Lust is hospitable despite his bleak outlook: he offers the visitors guidance, invites them home, and explains his world’s history. His decision to call himself “Lust” is almost self-mocking, reflecting his dislike of his own timeline 40 41.

Repeated failures have left him deeply discouraged. He describes himself as “the only sober one in a world of drunks” and initially considers further attempts to help meaningless. Nevertheless, he cooperates when Murder, Killer, and Insanity offer a concrete plan 42 44.

Papyrus is central to Lust’s willingness to endure life in the Underground. His anger at the monsters’ brutality softens when he thinks of his brother, and he has used lethal force to protect him. In the maze, however, Lust is wary and readily frightened by threats he believes cannot be destroyed 41 45 46.

Abilities & Skills

Scientific Research and Engineering

Lust studies timelines and soul traits and has practical experience building technology 40 42 48.

• Recognizes Murder, Killer, and Insanity as Multiverse counterparts after their introduction 40.
• Builds a device that suppresses his injected lust and conceals its presence 42 45.
• Investigates revived monsters through observation and attack tests, identifying their regeneration and lust-based detection 45 48.
• Lacks knowledge of the Determination Extractor because he was excluded from its experiments 43 48.

Shortcuts

Lust uses shortcuts to transport himself and companions between locations 43 44.

• Takes all three visitors to Alphys’s laboratory 43.
• Cannot use shortcuts inside Gaster’s soul-storage maze 45.

Combat Magic

Lust can use bone attacks and prepare magic for combat, though his attacks cannot permanently kill the revived maze monsters 46 48.

• Tests bone attacks against the creatures; even after being reduced to ash, they regenerate 48.
• Draws attacks from one or two monsters during the cleanup, allowing Murder to fight the others 49.
• Relies on Murder’s Anti-Determination to stop their regeneration; this technique is not shown as Lust’s own ability 47 48 49.

Telepathic Communication

• Speaks telepathically to Murder while hiding in the maze, asking him to increase the suppressor’s output 45.

Restricted Soul Access

• His direct relationship to Gaster allows him to open the barrier protecting the stored human soul 45 46.
• Uses that access to extract a small sample of the lust trait and reseals the container against the approaching monster 46 47.

Equipment / Weapons / Items

• Lust suppressor: A portable device of Lust’s own construction. It reduces his desire and can conceal nearby companions from monsters that detect lust. It cannot remove the trait completely, and he lacks materials for mass production 42 45.
  • Murder boosts it to 200% output with surrounding magic, allowing both of them to evade detection in the maze 46 48.
• Flashlight: Used to inspect a mutated monster while concealed by the suppressor 46.
• Comb: Used to groom his long hair 41.
• Syringe, temporarily supplied by Murder: Used to collect a sample from the stored human soul for the purification project 46 49.

Relationships

• Papyrus — His brother and a major reason he continues facing the Underground. Lust protects him from attackers and speaks warmly of his secret support for MTT 41 45.
• Dr. Gaster — His father and the scientist responsible for injecting the lust trait. Lust unsuccessfully sought his help and was excluded from his extractor experiments; their family relationship grants access to the restricted human soul 41 42 45 48.
• Alphys — A scientist Lust approached for help removing the trait. She had already succumbed to it, and he did not know about the True Lab beneath her laboratory 42 43.
• Murder — A Multiverse counterpart and partner in retrieving the soul sample. Murder strengthens Lust’s suppressor, saves him from an Amalgamate, and creates the Enchantment Web intended to purify the Underground 44 46 47 50.
• Killer — A visiting counterpart who reassures him that the group came to help and explains the extractor’s function and dangers 42 44.
• Insanity — A visiting counterpart who helps prepare the extractor and introduces the retrieved sample into it 44 49.
• MTT — A star whose mistreatment angers Lust. He knows Papyrus supports her behind the scenes in hopes that she can find salvation 41.

Story Role / Major Arcs

Meeting the Visitors

• Encounters Murder, Killer, and Insanity in a Snowdin alley after they flee pursuing monsters 40.
• Hosts them at the Skeleton Home and explains the origin of the Underground’s corruption 41.
• Shows Murder his suppressor, prompting the search for a machine capable of extracting soul traits 42.

Discovering the True Lab

• Transports the group to Alphys’s laboratory, where Murder uncovers the hidden elevator 43.
• Learns that direct extraction is unsafe: the machine processes only one being at a time and might remove a monster’s soul along with the unwanted trait 44.
• Agrees to help obtain a human-soul sample for Murder’s proposed mesh, intended for the Core’s ozonated water generator 44.

Retrieving the Sample and Clearing the Maze

• Guides Murder through Gaster’s maze and opens the protected soul container 45 46.
• Collects the sample, then survives an Amalgamate encounter with Murder’s help 46 47 48.
• Assists in eliminating the remaining creatures after Murder warns that continued mutation could make them a threat beyond the maze 49.

Preparing the Underground’s Purification

• Returns with the sample used to synthesize a material that selectively absorbs desire 49 50.
• Watches Murder form the Enchantment Web and is invited to accompany him to the Core. The supplied chapters end before the purification is carried out 50.

Notable Quotes

“That feeling of... being the only sober one in a world of drunks... it was truly sickening to the bone.” 42

“As it happens, I'm his son, so I can take the soul.” 45