The Daihasei Festival has begun, and that of course means that Tokiwadai Middle School—a prestigious all-girls' middle school—is competing too. Despite the participation of the Ace of Tokiwadai, Mikoto Misaka, the other students who are participating are still putting their utmost effort into winning, no matter how impossible the feat may seem against her overwhelming might. However, not all is fun and games. Due to the festival, Academy City opens to the outside world, and various factions have begun plotting ways to infiltrate the city. Misaka appears to be on their radar, and as the festival proceeds, people lurking from the shadows begin to emerge... Toaru Kagaku no Railgun T brings back the Tokiwadai Ace and her friends as they dive deeper into the dark side of Academy City. From terrorist attacks to ruthless underground projects, anything is possible in this city.

Entranced by surfing and the sea, Hinako Mukaimizu is a spirited girl who attends college in a coastal city with no consideration for her future career. Her life takes an unexpected turn when a fireworks mishap sets the apartment building she lives in ablaze, where she is saved by a talented firefighter named Minato Hinageshi. Upon meeting, the two quickly become acquainted with one another—Hinako is instantly enamored by Minato's reliable personality and passion for saving others, while Minato is intrigued by surfing and is eager to learn how. As Hinako begins to teach Minato about surfing, the pair eventually fall in love and begin a gentle and devoted relationship. However, while surfing may seem fun and carefree, it can still be a dangerous and unpredictable activity. This is what Hinako learns when a surfing incident completely changes her life, leaving her forced to contemplate her undecided future. In search of her own calling, Hinako begins her journey of self-discovery, keeping Minato by her side as she gradually attempts to find her purpose and ride her own wave.

With her late grandfather's inspiring words in mind, Chizuru Mizuhara teams up with her friend Kazuya Kinoshita to launch a crowdfunding campaign for an amateur film. The two hope that with the success of the project, Chizuru can honor her grandparents' wishes before she loses her grandmother as well. After their wild encounters with three girls—Kazuya's clingy trial girlfriend, Ruka Sarashina; their nosy new next-door neighbor, Mini Yaemori; and Chizuru's shy work friend, Sumi Sakurasawa—they all collaborate together to reach the campaign goal and begin production of the film. As their ambitious endeavor progresses, Chizuru and Kazuya grow closer and begin to struggle with their mutual feelings.

College student Miyako Hoshino is quite shy around other people. She mostly spends her time in her room making cosplay outfits. When her fifth-grade sister Hinata brings her classmate Hana Shirosaki home, Miyako instantly becomes captivated with Hana's cuteness. Miyako tries to do various things, ranging from making Hana wear cosplay dresses to giving her sweets. This gives Hana a bad impression of her at first, but Miyako will do anything to grow closer to the angel who has descended before her.