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1. Heart and Soul by DinofelisSnow1985

   Fandoms: Undertale (Video Game)  

   • Mature
   • No Archive Warnings Apply
   • M/M, Other
   • Complete Work

   22 Dec 2025

   Tags

   • No Archive Warnings Apply
   • Cross/Nightmare
   • Cross/Everyone (platonic)
   • Cross
   • chara - Character
   • Frisk
   • Papyrus
   • Nightmare - Character
   • Dream
   • Error - Character
   • Killer - Character
   • Dust
   • Horror - Character
   • Fresh - Character
   • Geno
   • XGaster
   • Reaper(mentioned)
   • Xtale Sans | Cross (Undertale)
   • Male Chara (Undertale)
   • Male Frisk (Undertale)
   • Papyrus - Freeform
   • Dreamtale Nightmare Sans (Undertale)
   • Dreamtale Sans | Dream (Undertale)
   • Error Sans (Undertale)
   • Killer Sans (Undertale)
   • Dusttale Sans (Undertale)
   • Horrortale Sans (Undertale)
   • Fresh Sans (Undertale)
   • Aftertale Geno Sans (Undertale)
   • Reapertale Sans (Undertale)
   • Sickfic
   • Sick Character
   • Terminal Illnesses
   • Street Rats
   • Abduction
   • Found Family
   • Near Death Experiences
   • Not Really Character Death
   • Suicidal Thoughts
   • Suicide Attempt
   • Sad and Happy
   • XGaster is a Jerk
   • Medical Experimentation
   • Unethical Medicine
   • Unethical Experimentation
   • BAMF Cross

   Summary

   Cross develops a terminal Soul disease, but his father only cares about his own reputation as a stellar Medical Scientist and uses his son(s) as lab rat to find a cure.

   Series

   • Part 7 of Nightmare's Clan

   Language:

   English

   Words:

   15,956

   Chapters:

   25/25

   Comments:

   64

   Kudos:

   232

   Bookmarks:

   26

   Hits:

   5,038