The Four Cardinal Heroes are a group of ordinary men from modern-day Japan summoned to the kingdom of Melromarc to become its saviors. Melromarc is a country plagued by the Waves of Catastrophe that have repeatedly ravaged the land and brought disaster to its citizens for centuries. The four heroes are respectively bestowed a sword, spear, bow, and shield to vanquish these Waves. Naofumi Iwatani, an otaku, becomes cursed with the fate of being the "Shield Hero." Armed with only a measly shield, Naofumi is belittled and ridiculed by his fellow heroes and the kingdom's people due to his weak offensive capabilities and lackluster personality. When the heroes are provided with resources and comrades to train with, Naofumi sets out with the only person willing to train alongside him, Malty Melromarc. He is soon betrayed by her, however, and becomes falsely accused of taking advantage of her. Naofumi then becomes heavily discriminated against and hated by the people of Melromarc for something he didn't do. With a raging storm of hurt and mistrust in his heart, Naofumi begins his journey of strengthening himself and his reputation. Further along however, the difficulty of being on his own sets in, so Naofumi buys a demi-human slave on the verge of death named Raphtalia to accompany him on his travels. As the Waves approach the kingdom, Naofumi and Raphtalia must fight for the survival of the kingdom and protect the people of Melromarc from their ill-fated future.

The all-girls Kikyo Private Academy and Chidori Public High School are polar opposites. With its prestigious history, Kikyo is attended by noble young ladies from distinguished families, while Chidori is infamously full of simple-minded delinquents. It is no surprise that their students clash with their differences. Having a tall stature and fierce appearance, Chidori student Rintarou Tsumugi is often avoided by others despite his gentle heart. One day, while helping out at his family's patisserie, he meets a customer who, after a brief moment, runs away from him. The next day, the customer returns to apologize to Rintarou, introducing herself as the cheerful Kaoruko Waguri. After spending time with Kaoruko, Rintarou appreciates that she does not judge him based on his appearance and looks forward to when they will meet again. However, when Rintarou discovers Kaoruko attends Kikyo, their relationship will challenge the social expectations and dynamics around them.

After surviving the entrance exams, Sakuta Azusagawa has finally enrolled in the same university as his girlfriend, Mai Sakurajima. He is gradually getting used to the unfamiliar environment as he attends student gatherings and makes new acquaintances. Everything seems to be going smoothly until Sakuta's friend and Sweet Bullet idol group member Uzuki Hirokawa begins acting out. With fellow Sweet Bullet member Nodoka Toyohama pleading for his help, Sakuta realizes that he has stumbled upon another case of the inexplicable Puberty Syndrome—Uzuki is feeling pressured by the sudden surge of popularity and rumors of a potential solo career. While Sakuta searches for a solution, another occurrence of Puberty Syndrome gradually emerges from the shadows.

The legendary former hitman Tarou Sakamoto has thwarted numerous assassins after an enormous bounty on his head was issued. But he cannot seem to catch a break and simply take it easy with his beloved family. A mysterious and infamous figure known as Slur has brought a group of insane death row inmates to Japan, who hold back from nothing to eliminate their targets. Sakamoto is not the only target—the criminals have been assigned to kill various other people, including the new hires at Sakamoto's convenience store, Shin Asakura and Lu Shaotang. The situation escalates even further when the Order, a group of the most skilled Japanese assassins, becomes involved. As the inmates begin wreaking havoc, Sakamoto and his allies must remain vigilant for the sake of everything they hold dear.