Seiken Tsukai no World Break takes place at Akane Private Academy where students who possess memories of their previous lives are being trained to use Ancestral Arts so that they can serve as defenders against monsters, called Metaphysicals, who randomly attack. Known as saviors, the students are broken up into two categories: the kurogane who are able to use their prana to summon offensive weapons and the kuroma who are able to use magic. The story begins six months prior to the major climax of the series during the opening ceremonies on the first day of the school year. After the ceremony is over, the main character, Moroha Haimura, meets a girl named Satsuki Ranjou who reveals that she was Moroha's little sister in a past life where Moroha was a heroic prince capable of slaying entire armies with his sword skills. Soon afterwards he meets another girl, Shizuno Urushibara, who eventually reveals that she also knew Moroha in an entirely different past life where he was a dark lord capable of using destructive magic but saved her from a life of slavery. Can those whose minds live in both the present and the past truly reach a bright future? Delve into the complex world of Seiken Tsukai no World Break to find out!

When a gate to another world suddenly opens on Earth, Mikado City is invaded by strange creatures known as "Neighbors," malicious beings impervious to traditional weaponry. In response to their arrival, an organization called the Border Defense Agency has been established to combat the Neighbor menace through special weapons called "Triggers." Even though several years have passed after the gate first opened, Neighbors are still a threat and members of Border remain on guard to ensure the safety of the planet. Despite this delicate situation, members-in-training, such as Osamu Mikumo, are not permitted to use their Triggers outside of headquarters. But when the mysterious new student in his class is dragged into a forbidden area by bullies, they are attacked by Neighbors, and Osamu has no choice but to do what he believes is right. Much to his surprise, however, the transfer student Yuuma Kuga makes short work of the aliens, revealing that he is a humanoid Neighbor in disguise. [Written by MAL Rewrite]

Murasame Sumika is popular in the high school for her excellence in the marks and sports. However, she has a secret: she is in love with her classmate Kazama Ushio. Ushio also has a liking to the love between girls, but she hasn't noticed Sumika's feelings and has always been refused by other girls.

As she heads off to her entrance ceremony at Sainotama Girls' High School, Akane Kikuchi muses over her grade school dream of becoming a manga artist and the lack of progress that she has made. When she finally arrives at school, she is surprised to learn that she is once again in the same class as her two best friends: the deadpan and emotionless Shiori Saginomiya and the hyperactive and ridiculous Nozomu Tanaka. Tanaka then comes to the obvious realization that she can't achieve her grade school dream of being popular with the boys and getting a boyfriend by going to an all-girls high school. In desperation, she begins asking the girls in her class to introduce her to their guy friends. Her classmates, however, are anything but ordinary. From a grandmother-loving loli to a reclusive chuunibyou to an overly analytical stalker, each one is given a fitting nickname by Tanaka to accentuate their weirdness. And so begin the wasteful days of these high school girls, each day kicked off with a simple question: "Hey, wanna hear something amazing?" [Written by MAL Rewrite]