When the threat of Earth being taken over by the Warstar aliens: Admiral Malkor, Prince Vrax and Creepox; Earth's guardian and Zordon's apprentice named Gosei and his faithful robot assistant Tensou recruits five teenagers to defend the planet as Power Rangers - Troy, Jake, Emma, Noah, and Gia. When the battle escalated, they would call on their individual assault vehicles named Mechazords and destroy the monsters who threatened peace in Harwood County, all while trying to live normal lives as high school students. The Megaforce Power Rangers use their Power Cards in their Gosei Morphers to call for their weapons, Mechazord and other assorted attacks and powers.
Mutants Bigs and Bluefur are recruited by Vrak and Robo Knight is awakened to fight them. Robo Knight was created by Gosei many years ago to protect the Earth but he didn't consider humanity part of the Earth. It took a learning curve provided by the teens to help Robo Knight learn and adapt to humanity. Robo Knight as Lion Mechazord calls the Knight Brothers Zords and form Gosei Grand. The Rangers try taking out the legendary Wild Sword out but Vrak took control of it. When the Rangers proved themselves to the Wild Sword, it became the Ultra Swords and provided the Rangers with Ultra Mode. With their new Ultra Mode, Bigs and Bluefur used the Aurora Box to become stronger and almost defeated the Rangers.
The Rangers were trapped by Bigs in a building abut saved by Gosei and Tenou who transformed their Command Center into the Gosei Ultimate Command Ship. The ship transformed into Gosei Ultimate and destroyed Bigs and Bluefur. Vrak then opted to use robots instead of mutants and built an underwater base along with Metal Alice. Metal Alice can build other robots and deploy Loogies. Metal Alice tried to convince Robo Knight to join her to no avail. Admiral Malkor was fed up with Vrak's failures and entered a cocoon to become stronger and fought the Rangers himself. Vrak used the Warstar spaceship and was seemingly defeated with Malkor by the Rangers. Metal Alice took him out of the wreckage and made him into a cyborg.
A robotic Messenger arrived on Earth to check on Vrak and helped him fight the Rangers. The Messenger was from Vrak's royal family and sending an armada. Vrak burned out the Rangers' morphers but Robo Knight re-syphoned his energy and de-powered the Messenger. Robo Knight was able to re-power the Rangers but left to charge up. The Rangers defeated the Messenger and Metal Alice. Unfortunately, the armada was arriving to Earth and attacking the Rangers. The Messenger warned Vrak to hide as he looked different and the armada might attack him. Troy wanted to look for Robo Knight and left the other Rangers.