One night right before summer vacation, Daichi Manatsu, a second-year in high school, sees a weird round rainbow floating in the sky above Seed Island (Shuushi/Tane Island) and ventures there alone. He has seen this rainbow before. With the memories of his father's mysterious death and an encounter of a mysterious boy and girl, Daiji arrives on the island while the alarm of a building labeled "Earth Engine" is going off. Someone asks him "Are you a captain?" just as robotic intruders from Uranus called "Kiltgang" arrive. The battle around the shining stars is about to begin.

Daichi was successful to unite the Earth Engine Impactor base formation. With a mysterious girl claiming to be "magical girl", he repel the Kil-T-Gang Morukin. Daichi's father was a Globe member once, he came back to the earth, knowing that it's organization protecting the earth from the invasion of aliens.

Yomatsuri Akari who is the only daughter of the Globe commander - Nishikubo - applied to the new team, they're enjoying the full summer of Tanegashima. In front of such four, a new enemy -Amarok- appears. Plateau with shaking off the restraint of Nishikubo,

Amarok and Moco from Planetary Gear commencing an assault on Globe base.

There are two factions divided over how to deal with the Kiltgang: the interception faction that wants to fight them and the ark faction that wants to send out a new humanity to escape. Commander Nishikubo, a member of the Interception faction, sends Teppei to rescue Eiji, the man who gave him his genes, aboard the orbital space station Tenkaidou.

Tippei's "father" has gone missing after the incident on the Tenkaidou. The "ark" faction seeks to allow a few chosen people to escape from Earth to avoid the Kiltgang. They try to steal Hana, because she is the key to their plans. Reito, who has been assigned as an observer to the Tanegashima base, tries to kidnap hana but is interrupted by Daichi, who stops him with his boomerang.

Just like Hana predicted, the Kiltgang appear inside defensive zone 1. Daichi is pinned between them and almost defeated, but Teppei and his Kiltgang Albion save him. Teppei destroys his own ego block, and with his help, Amarock and Moko are defeated. And after this success, Nishikubo authorizes the creation of a new intereception team, the Midsummer Knights, and names Daichi their captain.

After failing to attack Earth by themselves, Amara and Moco decide to awaken the other members of their race that are scattered to assist them. The first member they contact is Zin, the avatar of the robot Zimbalt and to confront him, Globe dispatches their newest unit composed of Daichi and his friends, the "Midsummer's Knights".

Ai, the avatar of the robot Aiatar is the second Design Child contacted by Amara and Moco, and to increase their chances of success, they kidnap Akari and force her to infiltrate mankind's orbital defense systems while Daichi confronts Ai with serious disadvantages.

Amara and Moco awaken Lin, the third of their companions and the Avatar of the Kill-T-Gang Liebam. Daichi confronts Lin and defeats her, but fails to prevent her from summoning Liebam and it's up to Teppei to stop her, piloting his own machine, the "Nebula Engine".

Akari and Hana befriend a young girl called Setsuna, unaware that she is one of the missing Design Children. Amara and Moco attempt to contact Setsuna, but stumble into a confrontation with Daichi and Teppei instead, while Setsuna learns the shocking truth behind the experiments made on her by her caretaker.