Set in a distance galaxy stars away from ours, it tells the tale of a war between the Galactic Federation and the Magellan Empire. At the core of the Federation is Planet Emperius, who take the brunt of the attack. The planet falls, but not before Prince Samson, the heir to the throne, takes a Last Stand against General Roboleon and is slain in the process.
His father, Emperor Emper, appoints the second of his sons, Prince Liger, as the heir to the throne in Samson's stead, while training his youngest son, Prince Yuger, for a new mission: legend speaks of a comet, Demon Star, that passes by Emperius every 950 years, and has the power to awaken the guardian mecha Daikengo, which may be their only chance at fighting back against the invaders. By coincidence, it is about to fly the very next day.
However, Liger has his own plans. Bequeathing his status as the heir to Yuger instead, he betrays orders to pilot Daikengo and becomes a rogue warrior. When the Magellan Empire offer universal peace in exchange for Daikengo and Liger refuses and dubs it a trap, Emper is forced to join the crusade against him.
With his childhood best friend Cleo, by his side and the help of his robots Anike and Otoke, Liger swears to fight for his kingdom and bring justice to the cosmos.
Space Guardian Daikengo (宇宙魔神ダイケンゴー) has examples of:
- Adjective Noun Fred: Uchuu Majin Daikengo or Space Guardian Daikengo.
- Alternative Foreign Theme Song: In South Korea, the series was known as Space Tyman (우주마신 다이켄고) and had a Korean-dubbed theme song
. - Artistic License – Space: The anime states that the galaxy has an edge to it, even though space is ever-expanding and is predicted to go on until the end of time.
- Bittersweet Ending: Daikengo saves Planet Empelius and the Robot Army is eliminated, but many of their Liger and Cleo's family members and loved ones are dead, several planets are left in ruins thanks to the war, and Liger never finds out the truth about his brother.
- Cast Full of Pretty Boys: In the setting of Planet Empelius, Long Haired Pretty Boys are the norm, especially royalty.
- Chekhov's Gun: Element 142, the rare Holocene material harvested from Planet Holostar, is the key to Daikengo's Mid-Season Upgrade and used in the Grand Finale to vanquish the Magellans for good.
- Comet of Doom: Inverted. The comet that passes Emperius every few centuries has the power to awaken the heroic Humongous Mecha.
- Contrived Coincidence: The Alien Invasion of the Magellans happens to occur around the same time the comet that powers Daikengo flies by.
- Does This Remind You of Anything?: At one point, Liger encounters a planet named Holostar that has chosen to take a stance of neutrality in the war, despite there being a clear aggressor. Their leader is called King Swizzler.
- Downer Beginning: Not only is Planet Emperius crushed by Magellan's military, Liger's big brother Samson also perishes while fighting to defend it.
- Excited Title! Two-Part Episode Name!: The Grand Finale, Fight! The Three King Star Swordsmen.
- Fanservice: For both men and women, though admittedly more for the former. For men, there's Lady Baracross, whose breasts the camera loves to ogle over. For women, Planet Empelius is full of scantily clad and hunk men (Pretty Boy/Bishōnen optional).
- Fantasy Counterpart Culture: Planet Katorian is inspired by Rome, based on the Roman style buildings and the fact that warriors from there wear traditional galea with thick red plumes.
- Forbidden Zone: The edge of the galaxy is nicknamed a "graveyard" and said to be a place where no one leaves alive.
- Giant Poofy Sleeves: The royalty of Planet Emperius all wear gaudy, large poofy sleeved clothes with frilly Regal Ruffs and spiky High Collar of Dooms that come in a variety of bright colours.
- Gray-and-Black Morality: On the gray side we have the politics surrounding Planet Emperius. Both Emperor Empel and Prince Liger want to do right by their nation, but Empel prefers to do it through peace negotiations while Liger would rather do it the old fashioned way, and Empel is forced to call a hunt on his son when he believes he's ruined Emperius' chance at tranquility forever. On the black side we have the Magellan Empire, that kill and invade relentlessly and spare no life, with Lady Baracross even murdering her most loyal subject, Roboleon, in the finale to save her own skin.
- Human Aliens: The Emperial alien race resemble humans, with the only things that make them stand out being the clothing and hairstyles.
- Insignificant Blue Planet: Earth is treated as this (despite many episodes taking place there) because it is distanced from the main conflict. Hell, it even avoids being part of the war for most of the show because the Magellans have that little interest in it. It's biggest significance is being home to Sabu, one of Liger and Cleo's friends, who usually fills them in on exposition about our planet.
- Karmic Death: Zakinder murdered Dr. Gooder because he saved the life of Prince Samson, therefore betraying the orders of the Magellan Empire. In turn, Bryman (Samson's new identity) finds him and kills him as revenge.
- The Reveal: Samson is Not Quite Dead, and Bryman is his new identity. He was saved by a dissenting doctor of the empire and remade into a cyborg.
- Shout-Out:
- Episode 16 has Liger travel to a planet called Arabida, which has a Prime Minister named Laurenz.
- The Robot Girl Liger and Cleo encounter in Episode 14 is an expy of Nana from Daimos. Their◊ appearances◊ are near-identical except for the Palette Swap, and they're both Little Miss Badasses from mecha anime.
- Succession Crisis: After Samson dies, Liger is propositioned to take the throne due to being the second oldest. It turns out that Liger doesn't want the throne either and is more interested in being a Warrior Prince.
- Melodrama: Moreso than the mecha fights, it focuses on the emotional tension regarding the rip between the royal family following Samson's death culminating one member going rogue and the King forced to put a death warrant on him, Cleo finding out that her beloved father is The Quisling, Samson's spirit being carried on by Bryman, many other planets' grudges against Emperius coming to light and Liger's struggle to make a name for himself alongside his older brothers.
- Was Once a Man: One episode has the Magellans launch an Alien Invasion on Earth and convert the humans they kidnapped into Brainwashed and Crazy Killer Robots.
- Wham Episode: Episode 20 has Liger and his father make amends. It also reveals that Bryman is actually Samson reincarnated.
