The series features colorful stop-motion mascot characters made out of pipe cleaners. In Japanese, "aiseki" refers to the situation of sharing a table at a restaurant with a person you don't know. The show is surreal datsuryoku-kei comedy with a variety of male guest voice actors who banter with Fuyumi and Haruko at a table in the Mongol Cafe.

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!

Ichirou Inuyashiki is a 58-year-old family man who is going through a difficult time in his life. Though his frequent back problems are painful, nothing hurts quite as much as the indifference and distaste that his wife and children have for him. Despite this, Ichirou still manages to find solace in Hanako, an abandoned Shiba Inu that he adopts into his home. However, his life takes a turn for the worse when a follow-up physical examination reveals that Ichirou has stomach cancer and only three months to live; though he tries to be strong, his family's disinterest causes an emotional breakdown. Running off into a nearby field, Ichirou embraces his dog and weeps—until he notices a strange figure standing before him.

Suddenly, a bright light appears and Ichirou is enveloped by smoke and dust. When he comes to, he discovers something is amiss—he has been reborn as a mechanized weapon wearing the skin of his former self. Though initially shocked, the compassionate Ichirou immediately uses his newfound powers to save a life, an act of kindness that fills him with happiness and newfound hope.

However, the origins of these strange powers remain unclear. Who was the mysterious figure at the site of the explosion, and are they as kind as Ichirou when it comes to using this dangerous gift?