Following their heroic efforts at Walter Park, the students of the misfit class return to Babyls Demon School after their summer vacation. What awaits them is not only adoration and admiration but also the shocking revelation that, in order to stay in the luxurious Royal One classroom, the entire class must be promoted to Dalet rank before entering the second year. As the Harvest and Music Festivals are right around the corner, there seem to be ample opportunities to rank up. Doing so will not be simple, however, as no class thus far has managed to accomplish such a feat. Hoping to give the misfit class a chance to achieve the improbable, the school appoints special tutors to aid in confronting the challenges that lie ahead. With his sights set beyond Dalet, Iruma Suzuki decides to take strides toward the goal of ranking up, starting with gaining acknowledgement from his special tutor: the short-tempered and selfish Bachiko Barbatos.

In the year 3990, the immortal Oldna Poseidal rules Pentagona, a war-torn solar system of five planets. Daba Myroad is a survivor of the Yaman Clan, just one of numerous native societies nearly wiped out by the tyrant. Living on the remote planet Koam with his friend Mirao Kyao, Daba possesses L-Gaim, a humanoid mecha known commonly as a "Heavy Metal" and the last known relic of the Yaman Clan. The pair befriend Fanneria Amu, an aspiring actress, and Lilith Fau, the last surviving fairy in Pentagona while on the run from a band of thieves attempting to steal L-Gaim. Daba promises to fulfill the dying wish of one of the thieves hunting him—an honorable act that leads him to the powerful merchant Amandara Kamandara. With their mission in sight, the ra group will face powerful adversaries and become entangled in a rebellion against Poseidal's reign.

A side story taking place somewhere before the second half of the series, prior to Daba acquiring the L-Gaim Mk-II. Daba's comrade Leccee is captured by Poseidal's forces, and Daba and his rebels attempt to save her.

Years after his father is defeated by an adolescent Gokuu Son, Magenta seeks revenge against Gokuu's family and allies. In his quest to resurrect the defunct Red Ribbon Army, Magenta drafts the services of Dr. Hedo, grandson of the evil legendary scientist Dr. Gero. Hedo embarks to invent a new line of superheroic androids to eliminate Gokuu after Magenta manipulates him into believing that Earth's most powerful heroes are actually alien villains. While Gokuu and Vegeta train offworld, the alien Piccolo mentors Pan, Gokuu's toddler granddaughter, in the same way he once trained Gohan Son, her father. Gohan himself has forsaken his warrior lineage in order to pursue an academic career. Both Piccolo and Gohan must leap into action when their quiet lives are interrupted by the arrival of Gamma 1-gou and Gamma 2-gou—Hedo's new android creations. While the Gamma androids believe they are fighting for justice, a more sinister project incubates beneath the Red Ribbon headquarters. Gohan and Piccolo take drastic actions to protect Pan and defend the planet against a new robotic menace.