The Arkean cataclysm

The Arkean cataclysm, sometimes dubbed the Sin That Led to Destruction was an apocalyptic event that befell the Arkeans. The Arkean Master and the Arkean Warriors had died, the average inhabitants were mercilessly killed as Arkea's core eventually collapsed completely and the planet had exploded, spelling the absolute destruction of the Arkean race, or so it seemed...

This was the era responsible for the many events that take place in Relic of Light.

Events
Following the Great Peace, Sinai had allowed himself to absorb the Darkness, greatly increasing his power. The Arkean Master caught wind of the event and tried to kill Sinai to punish his arrogance, but the newborn Arkean God's power had grown beyond control and destroyed the Master completely. Days later, the Arkean Warriors teamed up against the threat, only to fall themselves. The Arkean denizens tried to escape Sinai's campaign of hatred via the Twilight Zone, but the Arkean God had summoned a countless number of creatures known as the Shadows to hunt them down. Having nowhere else to run, the Arkeans surrendered. One by one, the Arkeans were devoured by the Shadows until none remained. Arkea's core collapsed during the massacre until eventually it could take no more, resulting in the planet exploding completely, spelling the eternal annihilation of the nigh omnipotent Arkeans.

Trivia

 * Although Lightsen himself was an Arkean, he mysteriously was not born until 100 million years after Arkea's destruction. Details of how this occurred are unknown.