Konran decided to hunt Taro. He had known of the master's whereabouts- high up, where the mountains meet the clouds. The Oni leaders at the temple threw a starting ceremony to wish the Overlord with luck and bless him. This ceremony consisted of displaying all three Oni Masks at the temple, and placing them on displays.
The Overlord underestimated his opponent's powers. When Konran arrived at the monestary, he was disguised within the body of a citizen. He soon burned the disguise, and the poor citizen's body was consumed by purple flames. Without a body, he appeared as a towering pillar of shadow. The two fought at the monestary, until Taro was able to ward off Konran. He fled.
Konran tried again several times at different locations. Once in the Forest of Tranquility. Did you know their fight there created the Fire Temple? Konran's yami powers and Taro's golden powers unearthed a crater of magma deep within the ground. Later, Taro built a temple there. They also had a struggle at the Caves of Despair, which caused the place to become unstable.
The Oni were being told of this by Overlord. They were unimpressed. They told him to pick up his efforts. And so he did. Because, in reality, he was power hungry and desired an army that could serve him. So he decided to make just that.
He traveled to the opposite end of Ninjago; the side where the Temple of Light was. Konran observed the durability and strength of the natural resources there. He chiseled stone to make heads, arms, legs, bodies, and more. Now, he just needed to bring these solid warriors to life.
Overlord used the yami to do this. It brought the stone warriors to life by inserting a lost soul into it. The reason why the Dark Island is filled with dark matter, yami, is because the Overlord flooded the island in order to submerge the warriors into it, and bring them to life. He crafted the Helmet of Shadows in order to ensure that he had full control. But he didn't wear it. He tucked it away in a hidden place. The Stone Army was born.
They invaded the rest of Ninjago. The Stone Army would murder victims, leaving their dead bodies nailed to the outer walls of their raided houses, blood streaming down. Eventually, they cornered the First Spinjitu Master in the very center of Ninjago.
"You have met your demise. Now you will join the Oni, your true master!" screamed Overlord as the Stone Army formed a circle around young Taro.
"Never! Ninjago is my home and my destiny lies here!" Steps were thudding against the ground as the fearsome Stone Army tightened their circle. General Kozu growled.
"FOOL! YOUR POWERS COULD BRING PEACE TO YOUR HOMEWORLD. YOU COULD BECOME A HERO," bellowed the Overlord as the Stone Army moved in closer.
"You'll never win. The balance cannot be corrupted!" protested Taro.
"Oh, but it can! GET HIM!" ordered the Overlord as his army charged at Taro.
"Yes master. Klacactu!" shouted Kozu in the ancient Stone Army dialect- a language that only they could understand. Taro put up a good fight. He fended off warriors, breaking them into shards. Then he'd repeat the process. But they kept coming!
He slashed, striking directly at the chest. Once the sword pierced through the warrior, their head would crumble and they would fall into pieces. He began to tire, however, as the opponents felt a surge and charged at once.
"The balance will be offset. Wherever there is light, there is shadow! And shadow shall overcome light for all of eternity!" whispered the Overlord softly, so only Taro could hear him. And then the warrior's circle shrunk. Except soon, the circle exploded.
I can't do this myself, the First Spinjitzu Master thought. This fight will have to be finished later.
And with that, he sent his sword down into the earth. Only he could hear the earth's howls and discomfort as a massive crack appeared in the ground. The ground began to swallow up the stone warriors. Konran was on one side of the crack, screaming at his stunned warriors. Taro jumped to the opposite side of the crack, and both sides of the land quickly drifted away.
"WHAT ARE YOU DOING?" the Overlord screeched as he was cast away with the Dark Island, where he would remain for millennia. Taro knelt down to the earth.
"I deeply apologize, Ninjago. An ancient evil has arisen. But I will vanquish him another day. I'm sorry, Earth," he whispered to the earth.
Nobody won the fight, and it would remain unfinished for millennia. The Oni soon found out about the Overlord's demise. They now had no way back to Oronai. They attempted to hunt down Taro themselves, but were driven to insanity and lost within the Primeval's Eye.
Meanwhile, their stronghold, the Oni temple, crumbled and deteriorated in their absence. Two of the three masks fell into the water stream and were lost in the jungle for centuries, until explorers discovered them. The third mask remained untouched at the Oni temple- until Lloyd Garmadon and the jade princess found it.
So there was peace in Ninjago for centuries now. But not in the Departed Realm. There were some… troublemakers. Therefore, I banished them and sent their souls to a newly made Cursed Realm.