Because Liveman has foiled every one of his disciples' plans and the conquest of the world keeps being delayed, Great Professor Bias finally decides to act himself, launching an operation called the "Giga Project". After careful study, Bias realises that Liveman has always defeated the giant Brain Beasts thanks to LiveRobo. If LiveRobo can be beaten, victory will surely belong to Volt. The Giga Project is therefore to build "Giga Volt", an invincible robot superior to LiveRobo in every respect.

First, he chooses "Giga Metal", developed by Kemp, as the robot's base material. Giga Metal is an extremely hard super-metal. Armed with a sword forged from it and first-class swordsmanship, the "Sword Brain" even defeated Red Falcon, the team's best swordsman.

Next, Bias needs a super energy source to power Giga Volt. He sends Mazenda to "Mount Bandai" in "Aizu", where vast reserves of lava energy lie beneath the mountain, to oversee the "Light Brain" as it extracts lava and refines it into "Giga Super Energy". However, the energy conversion produces massive radiation, which mutates the local insects into giants. This eventually draws Liveman's attention and they destroy the Light Brain, but by then Mazenda has already produced a considerable amount of Giga Super Energy.

With everything ready, Bias leaves Zuno Base alone, telling no one where he is going. In fact he has gone to a mysterious place deep underground to concentrate on the Giga Project. Because building Giga Volt causes huge tremors, he orders Guildos and Butchy to send out the "Earthquake Brain" to set off earthquakes everywhere, covering his tracks and distracting Liveman. Megumi's father, Yoichiro Misaki, comes from their hometown of Kumamoto, and with his support Megumi transforms into Blue Dolphin and defeats the enemy.

Although the enemy is beaten, the three sense that an even greater crisis lies ahead. In fact, this delaying operation has already given Bias enough time, and the Giga Project is nearly complete...

The skies darken, the earth shakes, and terrifying rumbles rise from below: all signs that the dreadful Giga Project has begun! Suddenly, in front of Yusuke, Jou and Megumi, a giant robot slowly rises from the ground. "Giga Volt" has finally appeared! At its controls is Kemp. By now Bias has returned to Zuno Base, confident that his masterpiece will wipe out Liveman in one stroke.

Giga Volt closes in on Yusuke and the others, and the three immediately face it with LiveRobo. True to its reputation as the masterpiece of the super-genius Bias, Giga Volt shrugs off every attack, even blocking the usually invincible finishing move, the "Super Beast Sword". Liveman is defeated, and LiveRobo itself falls into enemy hands.

At this critical moment, a cloud of dust rolls across the land and a huge mysterious tank appears with a roar of its engine. It launches a fierce attack on Giga Volt, which is caught off guard and cannot strike back. The tank takes the chance to rescue Yusuke and the others. Its driver is a young man who calls himself "Tetsu of the Bison", and the vehicle is the "Bison Liner". Volt sends a swarm of fighters to bomb the Bison Liner, and Tetsu is knocked unconscious.

The three rescue Tetsu, tell him how terrifying Volt is and urge him not to act rashly. Meanwhile, Giga Volt uses the "Giga Magnetic Field" on the unmanned LiveRobo, sealing it in completely. Yusuke and the others rush to the rescue, but Volt has the upper hand. Just as the three are about to be utterly defeated, another mysterious tank bursts out of the ground and attacks Giga Volt.

This tank is called "Sai Fire". Tetsu and the Sai Fire's driver are none other than the younger brothers of Takuji and Mari, who were shot by Kenji Tsukigata: Tetsuya Yano and Junichi Aikawa. Using the blueprints left by Takuji and Mari, and with the help of "Dr. Dorothee", formerly of Science Academia, the two built the Bison Liner and the Sai Fire, sworn to avenge their brother and sister.

Tetsuya is furious that Junichi arrived late. The Bison Liner's main circuit, the "A1 Circuit", had been destroyed by Giga Volt's bombardment, and the tank can no longer move. Yusuke suggests replacing it with the A1 Circuit from the "Live Cougar", and calls Colon to bring the Live Cougar at once.

Tetsuya happily takes the A1 Circuit Colon has brought, believing the Bison Liner can run again, when Kemp suddenly appears and blows it up. Face to face with their enemy, Tetsuya and Junichi charge at Kemp regardless of the danger, but they are no match for him. Just as they think their revenge is hopeless, Colon offers to try using the circuit inside her own body as a replacement. After much effort the Bison Liner starts up again and combines with the Sai Fire into "Live Boxer". Driven by their burning desire for revenge, the two throw everything into a furious assault on Giga Volt, pushing it into the Giga Magnetic Field and sealing it there. LiveRobo is set free, and Liveman's crisis is over for now.

After this failure, Bias orders Ashura to replace Kemp at Giga Volt's controls. Ashura uses Giga Volt to bombard the city at will. With no other choice, the Liveman warriors face it again with LiveRobo. In the middle of the fierce battle, a computer signal appears and paralyses Giga Volt. Radio waves from the battle had restarted the supercomputer of Science Academia, and the signal it sent was interfering with Giga Volt. Yusuke and the others rush back to the ruins of Academia Island and use the supercomputer to calculate how to combine LiveRobo and Live Boxer.

Then Dr. Dorothee arrives with an A1 Circuit. After talking it over with Jou and Megumi, Yusuke invites Tetsuya and Junichi to join Liveman. The two realise that Liveman carries the mission of protecting all humanity, not just fighting Volt for revenge as they had. Understanding this greater cause, they accept the transformation devices and become the new warriors "Black Bison" and "Green Sai". From now on, Liveman has five warriors!

LiveRobo and Live Boxer set out again and combine into Super LiveRobo. With its greatly increased fighting power, Super LiveRobo finally destroys the mighty Giga Volt.