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1. A Study in Intimacy by North_Light

   Fandoms: Undertale (Video Game)  

   • Explicit
   • No Archive Warnings Apply
   • M/M
   • Work in Progress

   16 Sep 2026

   Tags

   • No Archive Warnings Apply
   • Sans/Sans (Undertale)
   • Dreamtale Nightmare Sans (Undertale)
   • Something New Sans | Killer (Undertale)
   • Dreamtale Nightmare Sans/Something New Sans | Killer (Undertale)
   • First Time
   • Mutual Pining
   • Emotional Intimacy
   • Sexual exploration
   • sexual awakening
   • Inexperienced character
   • Inexperienced Nightmare Sans (Undertale)
   • Learning About Sex
   • As an asexual author I laughed at the irony of this
   • Awkwardness
   • Emotional Vulnerability
   • Developing Relationship
   • Something New | Killer Has Feelings (Undertale)
   • Dreamtale Nightmare Sans Doesn't Understand His Own Feelings (Undertale)
   • Nightmare Is Learning
   • Killer Teaches Nightmare About Intimacy
   • Emotional Hurt/Comfort
   • Explicit Sexual Content
   • Masturbation
   • Mutual Masturbation
   • Nudity
   • Touching
   • Tentacles
   • The tentacles tag is literally because of Nightmare
   • Teacher-Student Relationship
   • Slow Burn
   • Sort of Teacher-Student Dynamic
   • Sexual Tension
   • Ecto-Genitalia (Undertale)
   • Ecto-Body (Undertale)
   • Smut
   • Porn With Some Plot
   • Other Additional Tags to Be Added
   • Oral Sex
   • Praise
   • Praise Kink
   • Sort of Praise Kink Because Killer Doesn't Shut Up
   • Ecto-Penis (Undertale)
   • Ecto-Tongue (Undertale)
   • Ecto-Vagina (Undertale)
   • Ecto-Breasts (Undertale)
   • Sexual Overstimulation
   • Switching
   • Bottom Dreamtale Nightmare Sans (Undertale)
   • Top Something New Sans | Killer (Undertale)
   • Bottom Something New Sans | Killer (Undertale)
   • Top Dreamtale Nightmare Sans (Undertale)
   • Sexual Switches
   • Though Nightmare does bottom often...
   • Top/Bottom Versatile | Switch Couple
   • Vaginal Fingering
   • Squirting and Vaginal Ejaculation
   • Not all chapters have smut
   • Chapters with smut will be indicated by me on author notes
   • Domestic Fluff
   • Domestic
   • Dirty Talk
   • Flirting
   • Healthy Relationships
   • Safe Sane and Consensual
   • Porn with Plot
   • Porn with Feelings
   • BDSM
   • Light BDSM
   • BDSM Scene

   Summary

   Nightmare rescued Killer from a dying universe without giving much thought to what would happen afterward. Now Killer lives in his castle, disrupting centuries of carefully cultivated solitude with his emotions, his bad jokes, and an unfortunate tendency to get lost.

   When Nightmare discovers how Killer has been passing the time, curiosity gets the better of him.

   After all, Nightmare has lived for centuries without ever understanding intimacy.

   Perhaps it's time he learned.

   Language:

   English

   Words:

   9,921

   Chapters:

   3/?

   Comments:

   59

   Kudos:

   147

   Bookmarks:

   17

   Hits:

   1,511