|“So... this is the Realm of the First Spinjitzu Master. Soon, the power will be gone... forever.”|
|— The Omega to Garmadon and Lloyd in "The Fall"|
The Oni Invasion is an event in which the Oni invaded Ninjago by coming through the Realm Crystal and successfully taking over Ninjago City, petrifying many citizens who could not escape the city in time.
After the Oni successfully conquered the Realm of Oni and Dragons, Cloud Kingdom, and many other realms, they entered into Ninjago through the Realm Crystal, which was being kept at Borg Tower in a series of underground vaults along with several other artifacts such as the Serpentine Staffs.
After arriving in Ninjago, the Oni begin spreading their darkness, which petrifies any non-Oni and freezes them in place. The ninja rush in and save as many lives as they can, while they too struggle to escape. The ninja soon realizes that the only way to defeat the Oni is with another Oni, which prompts them to release Lord Garmadon from his cell in Kryptarium Prison.
Destroying the Realm Crystal and Gaining the Golden Armor
Shortly after releasing Garmadon, who tells the ninja the only way to defeat the Oni is to destroy the Realm Crystal, however after the ninja contemplates letting Garmadon go alone with a weapon they decide that Lloyd will enter the darkness with Garmadon. After Cole gives Garmadon a Katana, he starts a small battle with the ninja that results in his power returning. He then jumps into the cloud, with Lloyd following him. When Lloyd and Garmadon arrive in the cloud they see the frozen versions of the Ninjago citizens, however, they keep going until they reach the entrance to Borg Tower where they find a small group of Oni who attack Lloyd and Garmadon until Garmadon blasts them with his powers. They then continue into the Borg Tower Vaults. Meanwhile, the remaining ninja gets a distress call from Vinny of NGTV News who asks for help. The ninja separate from P.I.X.A.L., with P.I.X.A.L. taking her mech to wait for Lloyd and Garmadon to return while the others save the people trapped in the NGTV News building. Lloyd and Garmadon continue into the Borg Tower vaults until they come across the realm crystal covered in Oni tentacles. However, when they try to destroy it, a big Oni appears out of it who calls himself the Omega. Who, after questioning Lloyd and Garmadon, goes on to attack them. However, Lloyd and Garmadon fight back, but the Omega proves to be too strong for either of them to handle until Lloyd finds the Sword of Sanctuary, but when Lloyd tries to use it, he finds out that it has no effect on the Omega, but helps Lloyd destroy the Realm Crystal. Unfortunately, the destruction of the Realm Crystal does nothing and the Omega summons more Oni who attack Lloyd and Garmadon.
When Lloyd and Garmadon are cornered by the Oni, they believe that there is no chance, but when the Oni begins to tremble in fear and walk back, Lloyd and Garmadon realize the Golden Armor is behind them and that the Oni do not like Golden Power. They begin to use it to fend off the Oni. Meanwhile, the ninja continues to travel to the NGTV News building and evacuate everyone in time. However, the tentacles get closer and Nya pulls the Bounty's thrust lever the wrong way, making the Bounty propel backward. The sudden motion makes Cole let go of his ladder. However, he manages to take hold of it again, but only for the ladder to brake, which causes Cole to fall. Meanwhile, Lloyd and his father make their way out of Borg Tower and onto the streets of Ninjago City and are extracted by P.I.X.A.L. in her Samurai Mech, which is slowly losing battery life until the power goes completely out and they begin to fall until they are saved by the Bounty. After everyone is safe, the ninja tell Lloyd about Cole. Lloyd begins to mourn until Garmadon interrupts, in which Lloyd begins shouting at his father as he walks off. Later, Kai checks up on Nya who is sitting on the edge of the Bounty mourning Cole. After talking to Kai, she comes up with a plan to re-forge the Golden Weapons out of the Golden Armor, but she requires Kai's blacksmithing abilities, combined with his fire, to make it possible.
The Re-forging of the Golden Weapons
Shortly after returning to the Monastery of Spinjitzu where Faith has made a recovery, the ninja informs Wu about Cole's supposed passing. Wu mourns Cole's supposed death and begins to observe Kai as he reforges the Golden Weapons and gives Nya Cole's Scythe. Meanwhile, Cole has landed on the bottom floor of the NGTV News building and calls his Earth Driller to pick him up and drive to the Monastery.
The Final Confrontation With the Oni
After Kai reforges the Golden Weapons, the Oni, led by the Omega, march onto the Monastery where Wu, Garmadon, Faith, and the ninja (minus Cole) fight off against the Oni, but the weapons seem to be failing. Just when the Oni are about to destroy Lloyd, Nya, and Wu, Cole drills under the ground with his Earth Driller and knocks the Oni off the cliff. Meanwhile, Garmadon turns into Oni form and battles the Omega. However, after being blasted by the Omega, Lloyd calls a retreat, and the ninja all enter the Monastery. Jay then asks Nya to be his Yang and after seeing that they are probably going to lose. Lloyd comes up with a plan for all eight of them to form the Tornado of Creation, which they do and vaporize the Oni, destroying them and freeing Ninjago. Lloyd is transported to a faraway land where he meets his grandfather, the First Spinjitzu Master, who offers Lloyd the chance to go with him, so Lloyd tries to take his hand, but somehow ends up back home in Ninjago with his friends. Wu bids his brother farewell, and the ninja add a new Mural to the Monastery.
War of the Oni and the Dragons · Light vs. Darkness · Reign of Aspheera · Long Winter · Serpentine War · Battle for All of Time · Attack of the Great Devourer · The Final Battle · Nindroid crisis · Second Serpentine War · Battle of Stiix · Fall of Ninjago · Rise of Ninjago · Oni Invasion · Monastery Siege · Lloyd's Journey · Liberation of the Never-Realm · Attack from Prime Empire · Battle for Shintaro