Though he has successfully repelled the latest Wave of Catastrophe, Naofumi Iwatani—the Shield Hero—has no time to rest. Naofumi is spurred back into action when Queen Mirelia Q Melromarc tells him that the three other Cardinal Heroes have disappeared without a trace, and she tasks him with finding them. With no clues regarding their whereabouts, Naofumi tackles a more pressing issue: the worsening slave trade of demi-humans. Determined to right this injustice, he and his friends find their way to Zeltoble, the country of mercenaries, where the illegal sale of demi-humans has become a lucrative business. To gather money to free the slaves, Naofumi and his comrades disguise themselves and take part in underground coliseum brawls, purposely throwing matches to manipulate the odds and eventually secure an enormous payout. However, with the threat of another Wave of Catastrophe looming on the horizon, the Shield Hero must stick to his mission of finding the missing heroes if he wants to protect those he loves.

In a world where dead people turn into books and are stored in the Bantorra Library where anyone who reads a book can learn their past, Bantorra Library is maintained by Armed Librarians who wield psychic powers and their enemy is a religious society known as Sindeki Kyoudan.

Seikyou Private Academy, built on the intrigue of traditional occult myths, bears a dark past—for 60 years, it has been haunted by a ghost known as Yuuko, a young woman who mysteriously died in the basement of the old school building. With no memory of her life or death, Yuuko discreetly finds and heads the Paranormal Investigations Club in search of answers. A chance meeting leads Yuuko to cling to diligent freshman Teiichi Niiya, who can see the quirky ghost. They quickly grow close, and he decides to help her. Along with Kirie Kanoe, Yuuko's relative, and the oblivious second year Momoe Okonogi, they delve deep into the infamous Seven Mysteries of the storied school.

A long time ago, the ancient saviors of humanity founded a village as their haven, with their descendants said to assist humanity in times of extreme chaos. This village, Kunlun, is located just beside the infamous Last Dungeon—a place where monsters of unimaginable strength reside and which serves as the hunting grounds for Kunlun residents. Despite being accustomed to defeating powerful enemies since childhood, Lloyd Belladonna regards himself as the weakest in his village in terms of magic, strength, and intelligence. Even so, to fulfill his desire of becoming a soldier, he goes to the Kingdom of Azami to enroll in its military academy. However, as someone whose upbringing defies common sense, Lloyd's innate power might just prove to be the key to end the crises enveloping the kingdom!