Digimon Story: Lost Evolution is a role-playing game developed and published by Bandai for the Nintendo DS. Released in Japan on July 1, 2010, the game follows players as they raise and battle Digimon while restoring lost evolution data, introducing mechanics focused on recovering and rebuilding Digimon abilities.

The Digital World used to be a paradise for Digimon, until disaster struck. The Tamers who fought alongside Digimon and helped them grow have been going missing one by one... And the Digimon who were left found themselves being eyed by an unsettling group. In this time of crisis, Agumon decided to search for the Tamers by itself, and headed off to the Real World. On the night of a fireworks competition, a group of children headed behind the mountain to investigate a ball of light that had fallen there; that was where they met with Agumon. To answer Agumon's calls for help, the protagonist becomes its Tamer, and heads to the Digital World in pursuit of the mysterious trio who had abducted their friends. In a world they have never seen before, an adventure begins.