Deus Sin Machina
Grahf Fallen. The two words seem like a prayer in the months after his demise. Grahf, having wreaked havoc on the world, was finally slain by the Forgotten Four. As a result the Forgotten Factions went to war and many people died. The Forgotten Four even split, believing in and fighting for separate philosophies. Despite their undying friendship, the heroes participated in conflicting battles. The four never went up against each other during battle. They would face off against as many others as possible. However, there were casualities of old allies and new enemies alike. As the war raged on, the Forgotton Four went their own ways and suffered tremendous losses. Many of their family and friends fell in battle or as innocent bystanders. Furthermore, bitterness began to fill their hearts when they heard of a Forgotton One slaying one of their loved ones, as is what happened when Pipin’s prodigy, Davide, was slain in a one on one battle with Toph. Pipin consequently created his own universe of light and infused it with his own life energy, as a final sacrifice to save the ones he loved and as many innocents as possible. Thousands fled from the warring world into Pipin’s Sonic Realm, later dubbed the PSR (People’s Safety Realm).
After that, take a look at your wiki. There is some more helpful info there.