The simdroni (/ˈsɪmdrəʊni/) is a black, narrow-striped stranger with slender, pinkish hands and feet. It is smooth and somewhat warm to the touch, and a faint vibration can be felt when pressing firmly on it, although no particular motion is externally evident. It is uniformly composed of foamy, rubbery flesh that is pure black in color. The simdroni does not bleed when cut, but does expel a soft and almost invisible vapor in 4% of individuals. Regeneration is slow, taking up to ten weeks for even a thin cut to heal. Although the simdroni does not scar, markings are typically slow to reappear in injured areas.
In accordance with its reticent, subtle nature, the simdroni is odorless, lacks a mouth, and makes no sounds at all. In addition, it displays sound-dampening properties within three inches of its body, allowing it to move silently even over carpet or other rough surface.
The simdroni generates exclusively in single-person homes. Closed curtains, dark lighting, and quiet surroundings significantly raise the likelihood of a simdroni infestation, with frequent visitors or other social activities (such as phone calls or text-based communication) decreasing this likelihood. When the simdroni first appears, it is thin and small enough to fit in the palm of one's hand (with the exact moment of generation remaining unobserved). It appears beneath couches, under tables, or behind bookcases. Its growth is very gradual, and it may take up to ten years for a simdroni to reach full size.
The simdroni possesses a muted, subtle disposition. It spends its days at rest, and, although it is able to move, it remains relatively slow and inactive at all times. Any interactions with its environment are rare and random — every few weeks, for example, it might look at book titles, turn plates several degrees, or bury its fingers in carpeting. Otherwise, it prefers to silently observe the life of the person with whom it co-habitates.
The simdroni dislikes noise of any kind, and can even be weakened and killed by loud enough sounds. Sudden banging and crashing sounds cause it to cower and raise its arms in a protective gesture, although it does not display trembling or other signs of overt fear. Due to this aversion to audio, the simdroni, when able, silences any noise-producing objects within its territory, including radios, ticking clocks and even humming appliances. The simdroni is not malicious with this destruction, however, and instead, disables these objects with a careful, clinical precision.
The simdroni bonds to a single person, its presence atrophying communicative abilities in both sensitives and non-sensitives alike. While its target initially presents as relatively normal outside the home, as time goes on, they begin to spend more and more time alone, and these periods of silence and isolation become both longer and more frequent.
As the simdroni's influence becomes more prevalent, so too does its body grow longer and larger. Once the simdroni's body eclipses its victim's own mass, the affected individual loses all desire to verbally communicate, and as the stranger continues to increase in size, so too does its victim cease all attempt to physically communicate, as well. This effect is irreversible, and as the simdroni grows larger than the furniture around it, the victim loses the ability to recognize, relate to, or interact with other people altogether. If the victim is not physically moved, they will wither away inside their home, sentenced to a quiet, lonely death.
Although sensitives are aware of the simdroni's presence, and thus, have a greater chance to resist (and even destroy) the simdroni, they do experience the same symptoms as non-sensitives over a long enough timespan. Due to the simdroni's physically harmless nature, it is not unheard of for a sensitive to tolerate its presence, seeing nothing wrong even as their communicative abilities wither away to nothing.
"I went to visit my brother, just to make sure he wasn't dead. When I went into his house, he was there on the couch, right in eyeshot of the door, but, he didn't react to me, not at all. It wasn't like he was comatose, either — he kept looking from side to side, very slowly, then at the ground, but when I shook him, he didn't look up at me, but rather at some point just past my left ear.
And I stood up to get him a glass of water, in case he needed to take his pills, and right there, behind the couch, was where I saw the creature. It was long — stretching from one wall to the next, and curling a little to fit its tail through the bathroom's doorway. It didn't move or make a sound. I tried to touch it, and my hand felt right through, and I turned, and I asked my brother if he could see it, and he did not nod, and he did not shake his head, either, and when I turned back around, the creature was gone." Waka, Junko. The Hikikomori: A True Perspective, 169
The simdroni does not react to the actions of sensitives in any particular way, and does not retaliate when attacked, except to curl up into a defensive ball or cover its eyes with its hands.
The simdroni generates in a set of two 0.1% of the time. These pairs of simdroni are inert, and have no effect on people within their environment. These twins display a limited range of motions in comparison to their lone companions. As they grow larger, so too does each grow weaker and less active, until they stop moving completely, and fade away to leave behind a silhouette of their forms on the floor beneath them.
As the simdroni's victim grows catatonic, the simdroni begins to adopt some of their behaviours and routines. It will begin to crawl into their bed at night, pace from room to room in some diminished semblance of order, or stare at itself in the mirror each morning. The simdroni is killed once its victim is killed or removed, and the home in which it lives grows empty once more. As it dies, it turns to a black, gaseous shape, which fades slowly, leaving behind a dark stain that resembles a human being's shadow more than it does that of a stranger.