It is Universal Century 0087, and the One Year War between the Earth Federation and Principality of Zeon is over. The Earth Federation has created an elite task force, known as the Titans, who are responsible for hunting the remaining Zeon forces. However, the power-hungry Titans have shown themselves to be no better than Zeon, spurring the creation of a rebellious faction called the Anti-Earth Union Group (AEUG). 17-year-old Kamille Bidan lives in the colony Green Noa, home to a Titan base. Kamille gets in trouble after assaulting a Titan officer, an event that coincides with an attack led by former Zeon ace Char Aznable, now known as AEUG pilot Quattro Bajeena. When Kamille steals a Titan's prototype Gundam, he soon finds himself in the middle of the dangerous conflict.

Though Gundam Plastic Models, better known as Gunpla, exploded in popularity with the release of the anime series Mobile Suit Gundam, their presence faded before resurging with a new purpose. Through the power of Plavsky particles, fans are now able to pit their Gunpla against others in a virtual reality-style battle with the best competing at the annual Gunpla World Tournament. Sei Iori, whose father was a once finalist in the competition, dreams of one day conquering the contest himself. However, while Sei is an expert Gunpla builder, he lacks the prowess to effectively fight his creations during actual battle. In comes Reiji, a mysterious boy who is curiously ignorant of society but quickly demonstrates to Sei tremendous ability in Gunpla battles. The two boys decide to combine their strengths in order to sweep the Gunpla World Tournament and take the Gunpla world by storm.

Paradigm City, a city of amnesia and a place of belonging. It remains populated by forgotten pasts and the ruins of their labors due to a calamity 40 years ago. Shrouded in a fog-like mystery, it is up to people like Roger Smith to shine a light through the mist. Acting as a professional negotiator and suave agent, Roger is a self-tailored ladies man whose only love is for funeral black. However, as he gets deeply involved with his clients, what often starts as a simple negotiation evolves into Roger saving Paradigm from crime and peril. In the process, Roger stumbles even deeper into the untold folds of the city. As a rule, things are hardly ever as they appear. Serving as gray knight in a gray world, Roger is not without allies. By his side are Norman, a loyal and widely skilled butler, and Dorothy, a human-like android with deadpan snark. Together with the relic Big O, a jet-black mecha of gargantuan size and weight, they help Roger serve iron justice to Paradigm's lurking villains as he discovers the truth about 40 years ago.

Guided by her visions revealing the location of the King of Salvation, Jeanne Kaguya d'Arc flees with the polymath Leonardo da Vinci from the West Star to the East Star. There, she encounters Nobunaga Oda—the son of a local feudal lord who, following a brutal defeat dealt by an enemy clan, has sworn to conquer the world with his friends. Quickly convinced that Nobunaga is indeed the King of Salvation, Jeanne pledges allegiance to the Oda clan. Meanwhile, King Arthur, the ruler of the West Star, sends his ruthless general Gaius Julius Caesar and his combat machine army to conquer Nobunaga's planet and seize the Holy Grail. Although Kaguya believes that Arthur is the King of Destruction, the reckless behavior of Nobunaga The Fool—who named his own combat suit after his nickname—on the battlefield sows doubt in his capability as a leader. With the help of Himiko, the Yamato Queen, Nobunaga and his clan must unify in order to overcome tragedies, recover from betrayals, and eventually save the world.