The Ethereal Plane is coexistent with the Material Plane. The Material Plane itself is visible from the Ethereal Plane, but it appears muted and indistinct; colors blur into each other and edges are fuzzy.
While it is possible to see into the Material Plane from the Ethereal Plane, the latter is usually invisible to those on the Material Plane. Normally, creatures on the Ethereal Plane cannot attack creatures on the Material Plane, and vice versa. A traveler on the Ethereal Plane is invisible, insubstantial, and utterly silent to someone on the Material Plane.
Inhabitants of neighboring planes can’t perceive the Ethereal Plane at all, though certain mortals blessed or cursed with psychic sensitivity sometimes catch glimpses of its vistas. Since the Ethereal Plane is generally invisible from the other planes of the Inner Sphere, creatures under the effects of spells like ethereal jaunt and etherealness cannot be seen by creatures who are not themselves ethereal. Normally, creatures on the Ethereal Plane cannot attack creatures on the Material Plane, and vice versa.
Within the mists of the Ethereal Plane, warped, indistinct versions of locations overlap their Inner Sphere counterparts. This, coupled with the inherent weightlessness of creatures in the plane, makes it tempting to use the Ethereal Plane as a vantage to scout out unknown locales by passing through incorporeal walls and floating over traps with ease. The natural denizens of the plane make this a frightful prospect, however, and ensure that most forays into the Ethereal Plane are brief endeavors.
The twisted remnants of mortal souls comprise the vast majority of the Ethereal Plane’s inhabitants. Some souls, freed from their physical bodies by death, remain tethered to the Ethereal Plane by profound emotional distress and cannot proceed along multiversal currents to join the River of Souls flowing inexorably toward Purgatory until they sever the powerful emotional ties that bind them. Indeed, the longer these souls remain stalled on their afterlife journey, the closer they slide toward the Shadowfell, and the more of their memories and personalities become subsumed by raw emotional distress and psychic damage.
In a similar way that locations in the outside world possess overlapping etheric reflections, mortal creatures also have ethereal doppelgangers in the form of etheric doubles that exactly overlie their physical forms. The etheric double is a vessel for the cosmic breath of life that gives a creature animate force, most commonly known as ki. This energy collects in seven blazing vortices of colorful energy known as chakras, which bind the etheric double and the physical body together and distribute vital life energy to both. This energy extends 2 to 3 feet beyond the outlines of the creature’s physical form to create its aura, a nimbus of colorful occult energies that reveals much about a creature’s disposition and emotional state.
A creature’s etheric double, aura, and chakras are not visible except to those with the knowledge or magic to see them. From the Material Plane, this involves esoteric use of the Perception skill by a creature with the Psychic Sensitivity feat or any of a number of spells. From within the Ethereal Plane, all it takes to observe the interplay of these forces is simple concentration— if you know what to look for, it becomes plainly visible.
Interpreting this information, of course, is another matter. An etheric double is outlined in violet-gray or blue-gray luminescence. Unlike an astral body generated by astral projection or a lucid body of the Dimension of Dreams, an etheric double is not normally capable of acting as a separate vehicle of consciousness.