A Certain Scientific Railgun

Mikoto, Kuroko, Kazari, and Ruiko take action against a gang of bank robbers. When Ruiko is injured trying to rescue an innocent bystander, Mikoto angrily unleashes her railgun power!

Mikoto invites Kazari and Ruiko over to her dorm room to hang out, ruining Kuroko's plans of celebrating her one month anniversary since becoming Mikoto's roommate. Upon learning that Kuroko had ordered aphrodisiacs for the occasion, Mikoto ends up fighting her in the hallway, only for both of them to be caught using their power by the fearsome dorm supervisor. As punishment, both of them are sent to clean the school pool, where Mikoto is introduced to Kuroko's classmates, Kinuho Wannai and Maaya Awatsuki. As Kinuho offers to help Mikoto clean the pool with her aquakinetic powers as thanks for rescuing her from some thugs a while back, Kuroko gets jealous of how well Mikoto is getting along with others, believing that Mikoto has no use for her. To cheer her up, Mikoto gives Kuroko a present celebrating a slightly different anniversary, being the day when they became friends. However, whilst toasting, Kuroko accidentally drinks the aphrodisiac she had intended to give to Mikoto, becoming so overcome with lust that she steals Mikoto's underwear while she is still wearing them, prompting an electrical punishment.

Someone is tasering students and drawing on their faces with permanent marker! While Kuroko and Kazari investigate, poor Ruiko becomes the latest victim. Who is behind the unusual attacks?

Awkwardness ensues when Mikoto runs into Kamijo. When they meet again later in the day, Mikoto demands a duel! She gives it her all, but there’s a chance she’s no match for Kamijo’s powers.

Whilst out on patrol, Kuroko and Kazari come across a couple of petty thieves stealing from a car in broad daylight. However, when Kuroko charges in despite Kazari's warning, the thieves ambush Kuroko and injure Kazari as they make a quick getaway. Kazari scolds Kuroko for not only ignoring her warning, but also forgetting the promise they made together. Later that day, Mikoto is told the story about how Kuroko and Kazari first met in Judgment a few years ago. When Kuroko and her senior, Mii Konori, had gotten involved in a bank robbery, Kuroko's rash actions had led to Kazari being taken hostage by one of the robbers, an esper who can throw balls at a consistent speed, and had caused Mii to become injured protecting her from one of his attacks. Having realized her mistakes, Kuroko had managed to teleport Kazari outside to safety, staying behind to face the robber. In the end, Kuroko had been saved thanks to Mikoto, who anonymously answered Kazari's pleas for help, and had managed to apprehend the robber. In the process of telling the story, Kuroko remembers the promise she made with Kazari was to be true to themselves and become full-fledged members of Judgment together. Realizing her folly, Kuroko catches up to Kazari and joins her in pursuing the car thieves.

When an esper starts using gravitons to cause aluminum metals hidden inside stuffed animals to explode all over the city, Judgment struggles to find the culprit as the only esper whose ability matches the necessary level of the incidents is in a coma. Kuroko warns Mikoto not to do anything drastic like track down the culprit herself, but after Kazari leaves her Judgment armband behind, Mikoto uses the chance of being mistaken for a member of Judgment by Mii to show Kuroko that she too has what it takes to be in Judgment. However, she quickly finds being a Judgment member is not the exciting job she thought it was when she ends up doing a lot of menial yet difficult tasks. When the pair are later tasked to find a little girl's bag, Mikoto, assuming it is related to the graviton bomb case, takes drastic measures to retrieve the bag from a dog, only to discover no bomb was involved at all. Despite having her real identity exposed by Kuroko and Kazari, she is nevertheless thanked for her help, and by the end of the day, Mikoto has a new appreciation for a Judgment member's work. The next day, however, a Judgment member is injured protecting a civilian from a graviton explosion.