Atomos is a Pulse fal'Cie that digs underground tunnels along the Mah'habara Subterra. Its appearance is akin to a spherical boulder with a spinning circumference of glowing spikes. The fal'Cie also serves as a transport for whomever can stop it, possessing a partially hollow interior.
Atomos toils endlessly beneath the surface of Gran Pulse, ever extending the world's network of snaking, subterranean passages. Common speculation purports that the fal'Cie's goal is excavation of habitable underground environments, but the truth of the matter is shrouded in mystery.
What is known is that Atomos's digging often exposes deposits of valuable mineral resources. For this reason, the human inhabitants of Gran Pulse long ago established mining operations in Mah'habara.
Atomos is first encountered by the l'Cie party in the Mah'habara Subterra, when they are inside the derelict mining facility. Snow suggests they use it as a means of transport, and the party set out to do so. The party are aided by a group of Juggernauts, who work together to halt Atomos and save Hope Estheim. Afterward, the l'Cie are able to ride Atomos between the Mah'habara Subterra and the Sulyya Springs, as well as use him as a platform to access previously inaccessible parts of the mine.
After the fusion of Gran Pulse and Valhalla, Atomos appears to have made the Dead Dunes its final resting place. It forms part of a craggy area, and while it has become immobile, as seen in the Japanese Comic-Con trailer, its spikes glow during the night, showing that it is still active in some way. Atomos has rendered itself immobile, as if in response to God's will and quietly waits for the end of the world.
Atomos is the Greek word meaning "indivisible" and is the the origin of the word "atom" which means "that which cannot be cut."
- Atomos's model exists in the game disc of Final Fantasy XIII-2 in two versions, one close-up, more detailed model, and one model for viewing further away. Atomos never appears in the game, however, making the models dummied content.