Star Blazers consists of three television seasons. Each is an English-language adaption of its Japanese Space Battleship Yamato counterpart. However, the Japanese saga entails more than just these three television seasons, and part of this missing portion of the saga occurs between Seasons 2 and 3.
Star Blazers Season 1 is a straightforward English language adaption of the Japanese Yamato 1 television season. The plot opens in the year 2199, with planet Earth facing extinction within one year due to radioactive pollution caused by "planet bombs", the weapon of a blue-skinned, humanoid alien race known as the Gamilons. A message arrives from Queen Starsha of planet Iscandar, providing Earth with plans to build a superluminal engine and the promise that, if Earthlings can reach Iscandar, enduring what obstacles the Gamilons might put in their way, the Queen will give them a machine — the Cosmo DNA — that can neutralize the deadly radioactivity and restore the Earth's ecosystem. The challenge borne by the crew of the Yamato is to travel 148,000 light years to Iscandar and back to Earth in one Earth year.
In the late 22nd century, an alien race known as the Gamilons have attacked the Earth, bombarding it with radioactive bombs and forcing the population underground. However, the radiation is seeping into the planet; unless it's removed, Earth will become uninhabitable in one year. War with the Gamilons has also destroyed the Earth's space forces except for two ships – the Paladin, commanded by Alex Wildstar, and another ship, commanded by Captain Avatar. During a battle at Pluto, Avatar's ship is damaged. The Paladin gives Avatar's ship enough time to escape, but is destroyed in the process. This event becomes a major motivator for Derek Wildstar throughout the series.
Meanwhile, a non-Gamilon alien ship is hit in the crossfire and crashes on Mars. Cadets Derek Wildstar, Alex's younger brother, and Mark Venture investigate and discover a beautiful, dead woman, ejected from the escape pod and clutching a message capsule. They return to Earth in Avatar's battleship, and Derek notices the absence of any other ships. On the way back, they learn of Alex's fate. After they return, Derek confronts Avatar about Alex, but Avatar says it was Alex's decision to remain.
Cadets Wildstar and Venture return from their trip and are summoned to the Yamato, noticing that it looks brand new from underneath. When they board, they find themselves inside a newly modernized spaceship, commanded by Captain Avatar. Wildstar is eager to fight the Gamilons, but Avatar says that the ship's primary mission is to travel to Iscandar and return with the Cosmo DNA.