The Extra-Terrestrial Intelligence In Earth is the event which leads to the beginning of Thunder Force VI.
In 2161, the Extra-Terrestrial Intelligence made its arrival to the third planet of our Solar System, resulting in the invasion and first Extra-Terrestrial war between mankind and the aliens. As more battleships begain to warp on Earth's orbit, the U.E.G.'s forces are not enough to counter their attacks. Meanwhile in Babel, the scientists made a shocking discovery about Vasteel, the fragments of Vasteel Technology revealed the once called Vasteel was a starfighter known as "Rynex", created by an extraterrestrial force known as the Galaxy Federation. Along with the technology, there was four space coordinates, leading to the homeworld of the Galaxy Federation, and an interstellar call for help. To fight back the Extra-Terrestrial Intelligence and save both Earth and the Federation, mankind will have to use the once-forbidden Vasteel Technology. With no other choice, scientists and researchers restart the development of Vasteel Technology and the RVR program, resulting in the creation of the RVR-00 "Phoenix" and the Phoenix Brigandine.
This is when Operation 3 was formed. With the defeat of the Extra-Terrestrial ships in Earth's orbit, the Phoenix Brigandine made its "Gate" warp to the Galaxy Federation's star system, leading to the beginning of Thunder Force VI.