Sills

In the Nexus known as the Crooked House or The Station, the Set'i natives who built it have a natural adaptation for the layered and adjacent Realms that come together there. These Realms are not mutually hospitable to many life-forms and their physiology has learned to compensate. While no one has seen or has a memory of an adult Set'i in the last couple millennia, their larval form known as a Sill remain.  

Sills

  A Sill is a 2-8 cm long worm with a moist gray exterior, lacking eyes, limbs, or even a mouth. While many can be found throughout the Station, over the millennia, the larvae have formed a symbolic relationship with the (biological) denizens of Crooked House. When they enter the body of another biological creature, they gain safety, warmth, and sustenance. The host, however, not only gains the symbiont's ability to adapt to the changing environments, but also the ability to speak and understand (almost) any language with which they come in contact.  

On Arrival

  When a new biological enters the Station, they are greeted by a Welcome Bot, commonly called a WeBot. These WeBots come in many forms and shapes and are intended to choose to welcome a species that generally matches their own shape. The WeBot will briefly explain the nature of the Station, ask if there are any pressing questions, and then ask the new arrival to hold still as it places a Sill on their body near their mouth, nose, ear, or other available orifice. The Sill then climbs into the arrival's body and nestles itself in an appropriate location. For humanoids, this is in the chest cavity near the spine. The WeBot will insist that the fusion will not hurt and it's best to hold still. For most, this is true, and the process is commonly described as "strange."  

Limits of the Adaptations

  Adaptations to any environment in the Station are quick and seamless, but hardly comprehensive. The host may not necessarily be comfortable, but will be able to tolerate extremes of temperature, gravity, or pressure; breathe safely without regard for toxins, particles, or composition; tolerate types and extremes of radiation; and so on. Physical changes are limited to only those necessary to meet the needs of the environment.   Language, both spoken and written, are filtered through the Sill automatically, which alters the incoming perception and the outgoing expression. The host gains no actual knowledge of the languages being spoken, read, or written, but may observe the true interactions if they focus upon them. The language filter does not grant any cultural knowledge nor any physical ability to properly enunciate phonemes for which the host has no appropriate physiology. The language filter does work on gestural languages and some forms of telepathic communication, but only rudimentary ones.  

Effect on World Walkers

  A World Walker's natural adaptation ability is superseded by the symbiont's, though any environmental affinities are often not fully suppressed. The advantage to a World Walker is fusion with a Sill means their natural adaptation is not triggered constantly. As the process of metamorphosis is taxing and not necessarily immediate, this allows a World Walker to operate in Crooked House without potentially killing themselves or isolating themselves to a single (sometimes small) location and trying to never move.