The world envisioned and executed for the Mega Man Legends series is an amazing place. It's bright and cheerful, but not without its dark side. It's post-apocalyptic, yet warm and inviting. Grand and sweeping, yet detailed and personal. Set roughly in the year 51XX, it is the era known as Halcyon Days.

The planet known as Terra is a world covered almost entirely by water. The islands spread across its surface are pitted with crater impact sites, and many are littered with crumbling walls and giant remnants of ancient machinery. The inhabitants of Terra have built thriving towns and cities on these small patches of land, and travel between them by boat and airship. Their technology also includes automobiles, television, robotics, and radio communication. Their civilization is powered by quantum refractors, a powerful energy source harvested in ruins underground.

Dotting the islands of Terra (and sometimes protruding from the ocean) are small buildings called sub-gates, which house ladders or elevators that lead down into an entirely different world. This one is dark, ancient, mysterious, and inhabited by dangerous machines known as reaverbots. Reaverbots have been known to breach the surface in some places such as Calbania Island, but for the most part they are robotic subterranean guardians. Reaverbots come in many shapes and sizes to suit their function and environment. While some are known to be docile, the majority become highly aggressive toward any intruders who enter their dark domain.

Despite the dangers that abound in these ruins, they are continually explored, for deep within them are valuable artifacts and the highly sought quantum refractors. Those who dare enter the ruins to retrieve these treasures are known as diggers, who through their courage and skill, manage to keep the surface world supplied with energy. Serious diggers usually wear armor and combat the reaverbots with powerful arm-mounted cannons.

While diggers explore the depths, they are guided remotely by their spotters. A spotter helps choose the best route through the ruins, and monitors motion and energy readings that indicate the presence of reaverbots and refractors. Spotters and their scanning equipment are commonly set up aboard an airship that the digger team uses to travel from ruin to ruin. The airships themselves also consume the power of the refractors, and so the ravaging of the ruins continues on and on.

In addition to large refractors, diggers also collect refractor shards from reaverbots they destroy. When these shards are traded as currency they are called zenny, and form the basis of the economy, although gold also has great value. The wealth that makes its way up from the surface becomes the target of a different danger, air pirates. Like diggers, they travel the skies in airships and do battle with powerful weaponry, but for their own gain. In general, pirating gangs are known to have a few core members, and literally build their ranks with mass-produced robots who can perform a variety of tasks and pilot numerous ships and mechas.

An intriguing world full of mysteries bound to ancient technology needs one important thing to be whole: answers. Elysium (called Heaven in the Japanese version) is where those answers lie, a utopian world that orbits Terra like a second moon. It was created by the last remaining true humans, who for thousands of years lived there free of hardship and pain. Now, Elysium is under control of artificially created humanoid units, servants of the System, who monitor Terra and its population. The System has under its command smaller space stations able to descend to Terra and execute reinitialization on a local or global scale if the population of "carbons" grows beyond acceptable parameters.