The tomodari /toʊmoʊˈdɑːri/ is a brown and inanimate stranger with thin and slightly ridged stripes, and a solid body composed of a springy rubber substance. It almost always appears in a sitting, upright position, with a standing height of between three and four feet tall. This posture varies only slightly – 45% of tomodari hold one hand to their face, and 55% hold both. The base and tail remain affixed to the ground as though glued in place, and the stranger springs back to its original shape and position when pushed. If ripped off the ground, however, it dies instantly.

The tomodari always appear in linked pairs of twins, which generate at the same time. The distance between the twins varies; some form just a few feet from one another, whereas others appear hundreds, if not thousands of feet apart. Any wounds inflicted^ᵷ on one tomodari manifest simultaneously on the other. Though the stranger possesses minimal regenerative ability, this rate of regrowth is so small as to be unnoticeable only over the span of several years.

The tomodari is found in a wide range of locations, but prefers domed alcoves and other planes and voids which serve to amplify sound waves. Its generation is further aided by a constant level of low volume ambient sounds, such as a quiet alleyway around the corner from a busy square, a rooftop overlooking a schoolyard playground, or in the rafters above spacious conference halls and event centers.^ᶏ

It first appears as a pair of tiny, wrinkled lumps, which expand to full size within several hours. Rarely, one or more twins appear in a spot that does not allow an expansion to full size, such as beneath floorboards, or underneath a dumpster weighted down by cans of uneaten but expired food. In these instances, neither twin generates beyond a crumpled attempt.

The tomodari possesses an even-tempered nature. It does not move, and affects its world only passively.

Each tomodari acts as a speaker to broadcast the ambient audio picks up the other twin's location, projecting this sound from its upper body in a cone of sound radiating outward from its face. The sound of a bell chimed near one tomodari twin rings out from the mouth of the other, at a volume consistent with the original sound's level of volume, and with little distortion. There is no delay in this transmission, regardless of distance.

The tomodari is near a human corpse, its twin broadcasts audio in a voice that sounds all but identical to the deceased individual's former voice. The broadcast cycles through a number of vocal patterns, including laughter, angered grumbling, wordless singing, and fearful sobbing. The tomodari does not express language. This broadcasting continues until the body is removed or decomposes to a skeletal state.

As it ages, the tomodari's voice begins to deviate from the ambient audio its twin picks up. Ninety-five percent of tomodari divergence from the real sounds in only minor ways.^ᵵ In 5% of instances, the tomodari displays much larger divergences.^ℓ Both twins vibrate with daunted shivers following particularly violent outbust, but otherwise remain immobile.

The stranger displays the ability to move only at the very end of its life, when each twin, in unison with the other, lowers its hands from its mouth, yanks its tail up, and curls up on the ground. As the corpse dries out over the next days to weeks, its presence causes any living tomodari within a half-mile radius to project loud, distorted sobbing, which cease once the body decomposes into fine particles.