Insanity

Biodata

Background / History

Insanity previously pursued the thrill of killing through repeated cycles of resetting and slaughtering her timeline. She credits a second injection from the mysterious, hand-speaking ███ with restoring enough sanity to escape that pattern 30 42.

During this earlier period, Killer encountered her while in Stage 2 and attempted to kill her, assuming she was an ordinary Sans. Insanity retaliated with relentless attacks and chased Killer through several universes before Killer escaped. The encounter left Killer deeply afraid of her 31.

Insanity later fought a powerful human alongside another Murder and a LV1 girl who resembled them. When the three were close to defeat, ███ controlled Insanity and the girl, turning the battle in their favor until the human died. Remembering her own atrocities, Insanity intended to return home and reset her spacetime, but three Sanses intercepted her and demanded that she work for Nightmare 30.

Appearance

• Small stature: Has a young girl’s build and is shorter than Killer 30 31 40.
• Eyes: White light shines in her pupils; they contract when she enters combat form 30 32.
• Hair: Very long, heavily bloodstained, and apparently neglected when she first meets the main group 30.
• Hand: Bears a hole identified as a trace of ███’s control 30.
• Combat mannerisms: Displays an eerie grin, loud laughter, and persistent head-swaying during battle 32 36.

Personality

Outside combat, Insanity is comparatively calm, cooperative, and capable of recognizing her former instability. She reassures Killer that her earlier behavior belongs to the “old” version of herself, explaining that she now becomes crazed only when fighting 31.

In battle, she becomes aggressive and impatient, but remains tactically aware. She overwhelms Horror while secretly charging Shock Waves, rejects uv!Killer’s attempt to manipulate her through their shared origins, and scolds Killer for repeatedly stopping an attack whenever their opponent asks 34 36.

Her remorse develops into a commitment to make amends rather than simply erase consequences. She apologizes for drawing Murder and Killer into danger, then chooses to accompany them because she believes a casual reset cannot wash away her sins. Before the lunar battle, she also offers her pursuers a chance to back down, stating that everyone deserves a second chance 32 38 39.

Abilities & Skills

Combat Form

An adrenaline-driven state marked by contracted pupils, manic laughter, and heightened aggression 32.

• Her reflexes become so sharp that the world seems to slow from her perspective; this is presented as heightened perception, not demonstrated time manipulation 34.
• She can evade a close-range cleaver strike with a tight midair maneuver and counterattack immediately 34.
• Her principal advantages against Horror are reflexes and willpower, rather than superior raw strength 34.

Close-Quarters Combat

Insanity combines rapid punches, kicks, and weapon strikes to keep opponents on the defensive 34.

• Pressures Horror with repeated punches and lands a damaging kick despite his partial block 34.
• Knocks Horror unconscious by striking the base of his neck with a bone 34.
• Meets uv!Killer’s real knife with her fist, sustaining some bleeding but trapping the blade instead of retreating 36.
• Breaks Nightmare’s tracking device in half by bending it 37.

Durability and Endurance

Her earlier fighting style prioritizes trading injuries over avoiding damage 31.

• Killer recalls her HP appearing “practically bottomless,” but no numerical HP value is provided 31.
• Continues attacking despite direct contact with uv!Killer’s knife 36.
• Her endurance does not make her unbeatable: she seeks help because she cannot defeat all three pursuers alone, and Nightmare overwhelms the combined group 31 37.

Bone Magic and Shock Waves

Insanity uses summoned bones alongside physical attacks and charged magical cannons 34 36.

• Raises bones from the ground during her charge against Horror 34.
• Prepares a mass of Shock Waves while keeping Horror occupied in close combat 34.
• Summons airborne bones to knock away uv!Killer’s magical blades as they form 36.
• Uses both magic and close-range fighting to defend Murder from Nightmare’s tentacles 38.

Teleportation and Reset Access

• Teleports onto the Determination Extractor to adjust its settings and later inject a soul-trait sample 44 49.
• Intended to reset during her earlier fight with the powerful human before ███ intervened 30.
• Stops before personally resetting her home timeline and asks Killer to help with the reset while she leaves 39.

Technical Skills

Insanity assists with operating the Determination Extractor during the Underlust purification project 44 49.

• Adjusts switches and settings while Murder enters parameters 44.
• Works with Killer to prepare the extraction simulation while Murder and Lust retrieve the required soul trait 44 49.
• Injects the retrieved trait through a prepared opening, causing the extractor’s displayed sphere to shift from blue toward purple 49.
• Does not initially know how Murder intends to turn the resulting energy into an Enchantment Web 50.

Equipment / Weapons / Items

• Carried skull — Holds it during her meeting with Murder and Killer, then tosses it aside before the lunar fight; its identity is not stated 31 32.
• Brass knuckles — Appear in her hands when she prepares to fight uv!Horror 32.
• Summoned bones — Used as projectiles, defensive counters, and a handheld knockout weapon 34 36.
• Bill Sans’s surveillance device — Accepted as payment for being sent to potential helpers; allows Bill to watch the lunar confrontation through her vision 31 32.

Relationships

• Murder — The main-group counterpart she asks for help despite knowing he is not the Murder she previously met. He assists against her pursuers and accepts her into the group 30 31 39.
• Killer — Former opponent turned teammate. Initially terrified of Insanity, Killer later cheers her on in battle and welcomes her into their redemption journey 31 36 39.
• Other Murder / Murder from Triple Past — Fought alongside her against the powerful human and gave her comics and novels to read while they waited during that battle 30 49.
• ███ — The mysterious hand-speaking figure whose injection improved her sanity and whose control helped defeat the powerful human 30 42.
• Bill Sans — Sends her to Murder and Killer in exchange for surveillance access. His later rescue deal leaves all three obligated to attend a future feast 31 32 38 39.
• Nightmare — Wants her recruited into his team and attacks after she and her allies defeat his subordinates 30 37.
• uv!Murder, uv!Killer, and uv!Horror — Pursuers tasked with capturing her. She defeats uv!Horror and helps corner uv!Killer, who knocks herself unconscious to survive 31 34 36.
• Lust — Local Sans counterpart whose world she helps investigate and whose purification project she supports by preparing the Determination Extractor 40 44 49.

Story Role / Major Arcs

Triple Murder

• Seeking help: Meets Murder and Killer at Grillby’s after Bill Sans redirects her to them. She explains that Nightmare’s recruiters have pursued her across the Multiverse 30 31.
• Lunar confrontation: Waits on a moon with breathable air and comfortable temperatures. With Murder and Killer handling their counterparts, she takes on uv!Horror 32 33.
• Defeating the pursuers: Knocks uv!Horror unconscious, joins the confrontation with uv!Killer, and destroys the captured team’s Tracker 34 36 37.
• Nightmare’s arrival: Helps Killer protect Murder while he summons Bill Sans. Bill removes Nightmare and his three subordinates to another parallel spacetime 37 38.
• Joining the group: Leaves her home timeline to seek redemption with Murder and Killer, motivated by guilt and their shared obligation to Bill 39.

Underlust

• Scouting: Volunteers to explore outside Snowdin, then rejoins her companions after finding the local monsters disturbing. Builds a cardboard-box barrier around their hiding place before they meet Lust 40.
• Investigation: Connects Lust’s account of overwhelming desire to her own former obsession with killing and accompanies the group into the hidden True Lab 42 43.
• Purification preparations: Helps configure the Determination Extractor, completes preparations with Killer, and inputs the retrieved soul trait 44 49.
• Enchantment Web: Witnesses Murder use his special magic to form the mesh intended for the Core’s water system. The supplied account ends with the mesh completed and Murder preparing to take it to the Core with Lust 44 50.

Notable Quotes

“Everyone deserves a second chance, don’t they?” 32

“A lunatic like me... can’t wash away the sins I committed... with some casual reset.” 39

Trivia

• Her alias comes from other Sans counterparts rather than being introduced as her original name 31.
• After discovering comics and novels through the other Murder, she recognizes the trope of an important retrieval mission turning into a fight 49.