New Plane. A train plane. For the insane.

The Eternal Line is the train of destiny. It takes souls from birth, to childhood, to adolescence, to adulthood, to middle age, to old age, and to death, in that order. Everyone that lives has a shadow on the trains, and can replace that shadow if they enter the plane. When inside the plane, one can willingly get off at a station and remain there forever, having eternal life but being trapped on the platform. Attempting to leave a station will merely send you to another end of it. It is impossible to go back.

The rift out of the Line is the train, and can be entered at will once aboard.. The only way to leave is to get back on and let your shadow ride again, taking you on the journey to death.

The rift in is created when a soul is magically damaged. It and the body it resides in head to the Eternal Line. Damaging a soul generally requires high-end magics, but a soul with sufficient emotional damage can also create a rift. That level of emotional trauma generally requires a mental illness as well as a burst of repeated tragedy. The rift, when created, disappears after taking the person whose soul created it. The process lasts but a few milliseconds, and to observers it looks as though the body simply disintegrated.