Tony Stark, CEO of a large weapons manufacturer, physicist, engineer, and brilliant inventor, is wounded by shrapnel from one of his own weapons. While held captive by terrorists, he develops the Iron Man Suit and escapes. From that day on, he vows not to waste his second chance at life and to change the world for the better. For that purpose, he comes to Japan. In Lab 23 in Japan, great strides have been taken to develop, and build, a unique power station which does not run on fossil fuels, the Arc Station. Stark intends to join this project, and, for that, he is ready to announce his retirement as Iron Man. At the same time, he will also announce the Mass-produced Iron Men, to which he will pass on his duties. However, during the ceremonies, Stark is suddenly attacked by combat mecha belonging to an organization known as Zodiac.

In the distant future, humanity has found a way to live forever by purchasing mechanical bodies, but this way to immortality is extraordinarily expensive. An impoverished boy, Tetsurou Hoshino, desires to purchase a pass on the Galaxy Express 999—a train that travels throughout the universe—because it is said that at the end of the line, those aboard can obtain a mechanical body for free. When Tetsurou's mother is gunned down by the villainous machine-man hybrid Count Mecha, however, all seems lost. Tetsurou is then saved from certain death by the mysterious Maetel, a tall woman with blonde hair and a striking resemblance to his mother. She gives him a pass to the Galaxy Express under one condition: that they travel together. Thus, Tetsurou begins his journey across the universe to many unique planets and thrilling adventures, in hopes of being able to attain that which he most desires.

The Holy Grail War is a battle royale among seven magi who serve as Masters. Masters, through the use of the command seals they are given when they enter the war, command Heroic Spirits known as Servants to fight for them in battle. In the Fifth Holy Grail War, Rin Toosaka is among the magi entering the competition. With her Servant, Archer, she hopes to obtain the ultimate prize—the Holy Grail, a magical artifact capable of granting its wielder any wish. One of Rin's classmates, Shirou Emiya, accidentally enters the competition and ends up commanding a Servant of his own known as Saber. As they find themselves facing mutual enemies, Rin and Shirou decide to form a temporary alliance as they challenge their opponents in the Holy Grail War.

Asta and Yuno were abandoned at the same church on the same day. Raised together as children, they came to know of the Wizard King—a title given to the strongest mage in the kingdom—and promised that they would compete against each other for the position of the next Wizard King. However, as they grew up, the stark difference between them became evident. While Yuno is able to wield magic with amazing power and control, Asta cannot use magic at all and desperately tries to awaken his powers by training physically. When they reach the age of 15, Yuno is bestowed a spectacular Grimoire with a four-leaf clover, while Asta receives nothing. However, soon after, Yuno is attacked by a person named Lebuty, whose main purpose is to obtain Yuno's Grimoire. Asta tries to fight Lebuty, but he is outmatched. Though without hope and on the brink of defeat, he finds the strength to continue when he hears Yuno's voice. Unleashing his inner emotions in a rage, Asta receives a five-leaf clover Grimoire, a Black Clover giving him enough power to defeat Lebuty. A few days later, the two friends head out into the world, both seeking the same goal—to become the Wizard King!