A plague-like wind blows across the arid, sandy expanse of a post-apocalyptic Japan. As it sweeps over the living and nonliving alike, rust is all that remains in its wake. The cause of the catastrophic state of the world is believed to be mushroom spores. Bisco Akaboshi, known as the "Man-Eating Mushroom," is a wanted criminal archer whose arrows instantly grow mushrooms wherever they land. However, he is in truth a "Mushroom Protector," a person who spreads fungi in order to enrich the land and return it to its previous state. Alongside the crab Akutagawa and young doctor Milo Nekoyanagi, Bisco ventures through the wastelands of Japan searching for the legendary "Sabikui"—a panacean mushroom said to devour all forms of rust.

Individuals who can materialize weapons from their soul are called "Blazers," and they attend Kouryou Academy High School in order to harness their abilities. Each student is required to partner with another, in the hopes that one day, the pair can attain the power of Absolute Duo. Tooru Kokonoe hopes to attend this academy in order to gain power after his sister and friends were slain by a mysterious man. However, at the opening ceremony, he is forced to duel against the person sitting next to him, with the loser being expelled. As Tooru prepares to give the match his all, it is not a weapon that manifests from his soul, but a shield, an irregularity which catches the attention of a foreign student named Julie Sigtuna. [Written by MAL Rewrite]

After discovering that his orphanage was on the brink of closing due to financial stress, Finn, who was living freely on the streets, set out for a casino with the aim of making a fortune. However, nothing could have prepared Finn for the nightmare that was awaiting him. Once there, Finn encountered a car chase and bloody shootout caused by a man's "lucky" card. Finn will eventually learn what the shootout was about. The world order can be controlled by a set of 52 X-Playing cards with the power to bestow different superhuman powers and abilities to the ones that possess them. With these cards, people can access the hidden power of the "buddy" that can be found within themselves. There is a secret group of players called High Card, who have been directly ordered by the king of Fourland to collect the cards that have been scattered throughout the kingdom while moonlighting as employees of the luxury carmaker Pinochle. Scouted to become the group's fifth member, Finn soon joins the players on a dangerous mission to find these cards. "All you need in life are manners, dignity, and the will to bet on your own life." However, Who's Who, the rival car maker obsessed with defeating Pinochle, and the Klondikes, the infamous Mafia family, stand in the way of the gang. A frenzied battle amongst these card-obsessed players, fueled by justice, desire, and revenge, is about to begin! Are you ready? It's Showdown!!

We lay our scene in the fair Dahlia Academy, where two countries, both alike in dignity, come together; the "Black Doggies" of the Eastern Nation of Touwa and "White Cats" of the Principality of West have a longstanding feud. Romio Inuzuka and Juliet Persia, leaders of their respective dorms, seem to be bitter enemies. In reality, however, Romio and Juliet are hopelessly in love, but revealing their relationship would call upon the ire of all their comrades. They hide their love to maintain peace, but a clandestine relationship means they miss out on many of the activities couples get to do. As they grow closer together, Romio and Juliet must come to terms with the fact that keeping their relationship a secret may prove to be impossible. [Written by MAL Rewrite]