The insects of the world started to swarm for unknown reasons. To investigate this, Takuya Kai of the Earth Academia journeyed into the jungle and met Guru, a big rhinobeetle elder of the insect tribe, in a cave. Guru tells him that invaders, the Jamhal Empire, from another dimension are coming to take over the Earth, and that the insects are fighting to protect it. Takuya reassures him that humans will fight too. The Jamahl arrives on Earth, sending its generals and soldiers to start enslaving mankind. Daisaku and Rei, also members of the prestigious Earth Academia, save a girl from Jamar soldiers, but are captured. Meanwhile, at the Earth Academia, Professor Mukai and Takuya work on three prototype armor suits to help combat Jamahl.
Guru appears there and fuses three beetles into the suits, giving them life. The armors shrink and enter the three B-Commanders, and Guru tells them to select three warriors to fight Gaohm. One chooses Takuya, transforming him into Blue Beet and the others fly off to Daisaku to become G-Stag and Reito become Reddle. The three join forces to fight off the Jamahl forces. The leader of the Jamhal, Emperor Gaohm seeks Saint Papilia, a legendary savior with reviving abilities, to give him eternal life. The B-Fighters fight their jet planes with their Beet Machines, that board the Mega Heracles. During their war, the Jamahl clone Takuya to create Black Beet, his evil counterpart. He later searches for the Saint Papilia as well to have a full life since being a clone gives him a limited one.