The Oni weren't about to let young Taro escape their grasp for eternity. They wouldn't let the fabric between realms separate them from their eternal war and a hard-earned victory. Back in Oronai, the Oni were playing with dark magic. Magic that was never meant to be used.
You see, deep within the mountains in Oronai was a special material called yami. This same material was the very same "dark matter" that Garmadon used to corrupt Ninjago. Neither the Oni or the Dragon knew about the yami within the mountains- until the Oni found out.
They didn't know yami's true capabilities. Had they used it to its full potential, or in a different war, they would have won the war right then and there. They had never seen the purplish, slimy substance before. How would they know to use it correctly?
When Oni scouts returned one day with loads of yami, the top chemists were put to work to unlock the key to this new material. They did, and it didn't take long. Actually, the Oni discovered that the yami was made of lost souls. Modern historians conclude that Oni and Dragon lost in the mountains were killed somehow, and that they sank into the earth. Over the centuries, their bodies deteriorated into dark matter. Deteriorated into yami.
Now, when the Oni discovered it, they found that a spirit had been formed from the evil. It called itself Konran, and it appeared as a pillar of darkness and shadow. The Konran spirit was detained within a special stone while Oni leaders were informed immediately. Konran cried that he must meet with the leaders. After a few days, he was able to manipulate some guards into taking him to the leader.
Konran claimed that he had been created from the combination of lost souls. All of the evil and harm from these lost souls had been concentrated into one single spirit. He stated that he was powerful enough to warp between realms. The Oni promised him control of the Ninjago, Taro's land, if he could bring Taro back alive. Konran had no hesitation. He took on a new name. Overlord.
The Overlord opened a portal between realms. He and a few Oni leaders traveled to Ninjago, where they landed in the jungle known as Primeval's Eye. Using local materials and the rocks around, the Oni built a stronghold- the Oni temple. All three Oni masks were brought with them and kept at the temple. While the Oni leaders remained at the temple, Overlord was sent out to retrieve the First Spinjitzu Master.
The Overlord eventually did find the First Spinjitzu Master. When he found it incredibly difficult to defeat him, he took it so far as to create the Stone Army. But I will talk about that next. This particular story is too long to be confined within one simple chapter. Care to hear about the infamous fight between Taro and Konran?