Terichi

The Prime Material Plane is surrounded by the Outer Planes as we know them, and the 4 elemental Inner Planes. It is overlapped by the Feywild and the Shadowfell. However, a generation ago, this was not the case; there were 8 Inner Planes: the elemental planes, plus Life, Death, Magic, and Mundane. An evil god figured out how to bring magic into the Mundane plane and invaded it. He was killed there by its inhabitants, technologically advanced humans using nuclear weapons. A small group of humans recovered the god's heart and discovered magic. They used it to turn themselves into "heroes"; the resulting chaos caused the Magic and Mundane planes to collapse into the Prime Material, and Life and Death to be transformed into Feywild and Shadowfell respectively. Humans now exist on the Prime Material plane, and history has been rewritten so they have "always" been there. They are fundamentally different from the other humanoid races however, and the stability that has lasted for thousands of years has been upended.