The antheratrine (/ænˈðɛɹətriːn/) is a flat, blue and grey stranger with elongated eye markings and pupils that resemble a row of glowing white circles. Weightless but not formless, it seems to be made of a rubbery and indestructable material, and it lacks any internal constructs. Its appearance is ribbon-like, and the antheratrine is nearly invisible at a perpendicular angle, although the glow from its eye markings, though dim, carries at a distance great enough to be seen from the ground. The air around these markings is up to 15°F warmer than the surrounding air in a radius of up to ten inches.
It floats in the air, and is unaffected by almost all earthly movements, displaying no wavering in response to either wind or gravity. It does grow saturated during rainy weather, however, with this moisture drying normally once favorable conditions resume.
The antheratrine is predominantly mute (see interactions with sensitives).
The antheratrine fades into existence, mature at generation, at altitudes of above 15,000 feet. It is stationary during this generation, assuming motion only after a full 24 hours have elapsed.
The antheratrine's disposition is resolute. It follows jetliners and other commercial aircraft traveling at great speed, stretching longitudinally to match the length the craft it follows. It does not leave the confines of the city in which it appears, and once an aircraft leaves its territory, the antheratrine doubles back and travels in long, straight lines until it has caught sight of another vehicle.
When two or more antheratrine meet, the younger always follows the older of the two. The pursued antheratrine appears at first indifferent, but, as times goes on, it begins to deviate from its straight paths, turning and twisting through the air. The pursuant antheratrine picks up speed in response, circling its companion. This "dance" continues for up to several days, each circumlocution causing the two individuals to fly closer and closer together. Their now-looping paths become more complex and geometric until both individuals become tangled as one, at which point they cease motion and fade away prematurely.
Any sensitive within 1,732 feet of the antheratrine experiences, to varying degrees, a pervasive sense of calm and untroubled "worldliness"1. A third of these sensitives also experience a specific audio sensation sounding like a word2 or short phrase associated with this feeling, spoken in a neutral voice and repeated during the length of this encounter. This voice is equally likely to sound like either the sensitive's own voice or that of an unrecognized stranger.
The antheratrine itself has no visible response to a traveling sensitive.
After no more than 40 days and nights, the antheratrine fades away and leaves nothing behind.