The Guardian is the villain from Thunder Force V.
In the year 2106 A.D., the research probe Sekika-3 finds what it seems to be a spaceship drifting in the Oort Cloud, a comet belt in the outer limits of the Solar System. The probe returns to Earth in 2108, along with the mysterious ship. The ship is sent to a lunar base of the World Unified Government to be studied by the brightest scientists from the world. The ship is named The Vastian's Steel, or simply Vasteel. Earth's technology advances at an astounding speed in the following decades, thanks to Vasteel's technology.
In the year 2139 A.D., most of Vasteel's secrets remain unknown, so the scientist decide to create a supercomputer to further analyze Vasteel. A gigantic man-made island is created in the South Pacific called Babel, where they house Vasteel and the supercomputer, which is named The Guardian. Guardian's amazing AI is able not only to analyze Vasteel's complex systems, but also to implement it's technology. By the year 2145, humanity is already able to travel into space, so the World Unified Government tasks Guardian with the creation of a fleet of starcrafts, while they search and select planets for colonization. However, they fail to tell humanity that the starcrafts created by Guardian were in fact heavily armed battleships, bristling with experimental Vasteel weaponry.
During the year 2150 A.D., the Turing Code, a security program that dampened Guardian's AI so a certain degree of external control could be maintained, was mysteriously deleted from Guardian's systems. As a result, Guardian acquired sentience and free-will. For reasons unknown at that time, Guardian declared war against mankind. It had already built tons of highly-advanced weapons using Vasteel technology, so Earth was defenseless against Guardian. The few weapon under control of the World Unified Government were easily disabled by Guardian, who hacked all computers in the planet. The reasons for Guardian's declaration of war were unclear, but analysis of the final data streams transmitted from Babel revealed that Guardian went rogue shortly after initiating an analysis of Vasteel's holographic memory-storage unit.
The World Unified Government launches a massive attack against Babel, but it only resulted in the death of thousands of soldiers. The only weapons at their disposal that could withstand Guardian's attacks were the ones with Vasteel technology, and even so they were few, since most of Vasteel technology was under Guardian's control. Guardian's attacks, which were named the First and Second Annihilation resulted in a massive onslaught that took the life of one-third of Earth's populace. In a last effort to stop Guardian, the World Unified Government scrapes their remaining resources to create a combat unit they named “Thunder Force 222”, comprised of only seven units of the RVR-01 Gauntlet starfighter, which was a perfect copy of the original Vasteel. They select the best pilots from the “Circulate Death” program, a cloning program created with Vasteel technology, to pilot the ships and attempt to stop Guardian at all costs.
The combat unit, commanded by Cenes Crawford, is tasked to attack and take control of key areas that were under Guardian's control. The mission was considered a suicidal mission, and their chances of even surviving the raid were deemed to be extremely low. However, against all odds, the team is successful in destroying all Guardian's forces in Earth. Their last target was the Sword Fleet, a massive fleet controlled by Guardian in the orbit of Earth. They are once again successful in destroying it, however Cenes realizes that they were actually being hustled. Somehow, Guardian was letting them win, making poor tactical decisions and fleeing battles even when it had an overwhelming material advantage. In a bizarre turn of events, Guardian hacks into WorldNet and destroys every single bit of data that was related to Vasteel. The group then realizes that Guardian wanted to destroy all Vasteel technology, including itself.
The group then tasks Cenes to pilot the RVR-02 Vambrace, a more powerful version of Gauntlet, to infiltrate Judgment Sword for the final battle against Guardian. She finnaly destroys Guardian for good, but Guardian send a message to Cenes before being destroyed. In this message, it begged Cenes to destroy Vambrace, for the sake of humanity. The ensuing explosion of Judgment Sword send Vambrace drifting into outer-space. Cenes uses the remaining power on the ship to sen a radio transmission to Earth. In this transmission, she tells that Vasteel's real name was Rynex. Guardian knew something about Rynex that nobody else did, and that something on Rynex was what corrupted Guardian. Somehow, Guardian overcame this influence, allowing itself to be destroyed. As Cenes ends the transmission, she self-destructs Vambrace, thus ending the Vasteel technology.
- The Rynex is actually the ship from Thunder Force IV. It is implied that the mysterious force inside Rynex that corrupted Guardian was actually the remaining data from Khaos, which it uploaded into Rynex before being completely destroyed.