In the original storyline as aired in Japan, Dairugger XV was simply an exploration robot, as well as an intended peace-keeping force. The Earth is in a time of prosperity. The president of the Terran League (the "Galaxy Alliance" in Voltron) launches a mission to explore beyond the galaxy. After commencing its mission of exploration, the starship Rugger-Guard is attacked by a ship of the Galbeston Empire. Dairugger, the super robot, is deployed in order to defend the Earth. It is somewhat by fate that they must help the people of Galbeston find a new planet before it explodes, and liberate it from its despotic Emperor. In the Japanese version, it does not have anything to do with King of the Beasts GoLion, as opposed to the U.S. version, Voltron: Defender of the Universe. There are three assault team units: Land, Air, and Sea. There are a total of 15 parts referred to as "Rugger," which can combine together to form the super-robot Dairugger. The design of the 15 separate Rugger units came from the sport of rugby, since 15 players are required to form a rugby union. The U.S. version would rename the "Galbeston Empire" to "Drule Empire," along with editing a fair amount of violence and sexual content to keep the show safe for general audience broadcast.

A criminal group known as Demon Seed terrorizes Tokyo with its vast armies of mecha. The local police is afraid to confront them, but one person stands in their way: Maron Namikaze, a 13-year-old idol singer with a catchy voice and unbelievable superhuman strength.

To save the Earth from alien invaders and their giant monsters, Dr. Kishida does what any other red-blooded mad scientist would do: he builds a giant robot—the ultimate feminine fighting robot! Unfortunately, his grand-daughters refuse to pilot it! Apparently, they've got more important things to do than becoming teenage super-heroes. Besides, how are you supposed to study for your college entrance exams while getting beaten-up in battle? Fortunately for Dr. Kishida, things aren't too well for the invaders, either. According to their reports, the Earth was the perfect target: lush, peaceful, and relatively defenseless. Theoretically, the planet should've surrendered long ago. Now, the war is at a standstill, the dreaded Accounting Department is warning about the serious cost overruns, and the head of the home office has arrived from Galactic Headquarters to personally oversee operations. Has Headquarters decided to unleash, The Audit—or do they have something even more evil in mind? The fate of the world rests upon two people: Aya Kishida, one of the doctor's granddaughters, who may have to give up prep school to pilot the mighty (and lovely) ARIEL; and a mysterious alien named Saber Starblast, who may have the power to defeat the invaders once and for all...

Those incompetent aliens are still plotting to conquer the Earth! The only obstacle in their path is the giant, feminine robot ARIEL! But the young pilots have lives of their own... When Kazumi receives a mysterious love letter from a secret admirer, should she cancel her first date just to save the Earth?