Academy City is a highly developed place in terms of technology. It is said to be 20 to 30 years ahead of the rest of the world. Eighty percent of its 2.3 million residents are students. The focus of studies here is directed towards esper powers. Misaka Mikoto, one of the top level espers in town, shares a room with Kuroko Shirai, another high level esper who is a member of Judgement, a law enforcing agency composed of students. Both attend to Tokiwadai, a private school reserved for the high-leveled and the rich. Kuroko's partner at Judgement, Kazari Uiharu, is a low level esper who studies at Sakugawa middle school. Her best friend and classmate there is Ruiko Saten, a level zero (no esper powers). Together, the four encounter several adventures in the exciting scientific town.
Mikoto Misaka, one of the strongest Level 5 espers in Academy City, gave her DNA map to a certain doctor when she was young, believing that it may be used for greater good. Unfortunately for her, it ended up being used to create countless clones of herself; forming the Misaka network, in order to create the strongest esper by sacrificing these clones whom she considers as her own sisters.
Advanced placement into a school of higher grade proof-reading is determined by the results of the Promotion Test strictly for class type. Ranging from A class with the best facilities anyone can offer all the way down to F Class which is composed of low dining tables, rotten tatami mats and other worn out facilities. Students can change classes by competing using the Examination Summons Battle system or ESB. Students summon characters with their equivalent test mark scores and use them to compete with other classes.
Akihisa Yoshii, now in his third year in high school, continues his misadventures with Yūji, Mizuki, and other high school friends. Akihisa, however, is enrolled in a rather unique high school. In Fumizuki Academy, all of the students are given avatars with fighting abilities whose power reflects the student's academic success. With their avatars by their side, our characters explore deeper into what it means to be a friend and how they treat each other and why. While Shoko, the school's #1 student, endlessly tries to woo Yūji, Minami and Mizuki try to capture the romantic attention of the oblivious Akihisa.
Squid Girl has come to the land from the depths of the sea to conquer humanity for its pollution of the ocean. Unfortunately she ruins the first house she uses as an invasion base and has to work to pay for repairs. Of course, she can't overcome the Aizawa sisters who manage the house, so who knows whether she can subjugate humankind.