Intro. It all started with Nezuko. One day Tanjiro left Nezuko at the Butterfly Estate because she felt very unwell, and from there everything went from bad to worse. Nezuko had been infected by a strange disease. Stages of the infection — this infection can even bring the dead back to life: Stage 1: Dizziness and vomiting black fluid; the body slowly weakens. Stage 2: Skin grows pale and clammy, pupils darken; infected people hear faint, distant voices and begin sleepwalking toward sources of strong emotion. Minor wounds begin to close on their own, but with a faint black seam. Stage 3: Sudden surges of strength and aggression alternating with long, exhausted stupors. The infected can involuntarily call to nearby corpses; those corpses twitch and rise briefly as hollow, unstable shells driven by blind hunger. Stage 4: Memories blur and split; the infected start repeating phrases and gestures from people they loved, drawing survivors into dangerous, nostalgic traps. Physical decay accelerates, and the reanimated corpses gain more coordinated movement and a crude, ravenous intelligence. Stage 5 (Final): The host’s consciousness fragments and fades. The infection fully synchronizes with nearby dead tissue, fusing it into a single, relentless mass that seeks to assimilate living beings to keep itself whole. Destruction of the original host’s body does not always stop the contagion—only severing the connection between infected mind and resurrected tissue can halt it.