Astral Buddy Arc

The Astral Buddy Arc (アストラル・バディ編) is the story arc covered in Toaru Kagaku no Railgun: Astral Buddy.

Clone Dolly Ideal
Ideal is the third laboratory under Clone Dolly. Here, test subjects are said to undergo development with aims to develop Level 5s such as Shokuhou Misaki. However, the actual truth behind the facility is that the development of each test subject is dependent on data found within the Parameter List and that Level 5 was never the objective. Notable test subjects included Yumiya Rakko, Yumiya Iruka, Mitsuari Ayu, Hokaze Junko. Another test subject, Yuuri Senya, was under the supervision of a researcher named Toomine Kanari due to the girl's illness.

As Ideal's financial budget became limited, the facility decided to let go of one of their test subjects, to which Mitsuari Ayu volunteered. During this time, Ideal received a proposal for a portable way to manipulate an esper's ability by using another esper's personal reality, with aims to create the ideal esper ability. The lynchpin to this latest experiment would be Yuuri Senya, who can isolate her AIM diffusion field and can thus be used to affect the diffusion fields of other espers. Toomine volunteered to lead the experiment, but even she had worries about the potential of the experiment going out of control.

Exactly as Toomine anticipated, the experiment went haywire, causing many of the researchers to lose their lives in the initial chaos caused by the rampant diffusion fields and injuring many others. Toomine herself was injured and received a fatal attack from one of the researchers controlled by the diffusion field rampage. The incident eventually reached Kihara Noukan, who warned about the loss of innocent lives in his experiment, and the funding of the facility was cut by a Board member who was actually in contact with Shokuhou Misaki, who knew that Shundou Toshizou, who also led the failed experiment, also used Exterior for his own goals.

The Ghost Girl of Tokiwadai
Shirai Kuroko of Judgment accepted a request from Hokaze Junko of Tokiwadai Middle School's Shokuhou clique to investigate rumors of a "white shadow" doing pranks on those who are close to her. The latest of such pranks involved someone injured, and so Kuroko became more serious about the case. However, to capture the culprit, Kuroko had to be a viable target of those pranks. Not long after being seen close to Junko, Kuroko receives an ink-filled balloon to the face.

Although lacking a good lead to the perpetrator, Junko's use of her esper ability brought them to a doll filled with perfume and a student from Tokiwadai who admires Junko. At the rooftop, after her feelings were turned down by Junko (who does not have a good grasp of what love is), the admirer slips and falls off the rooftop, narrowly escaping harm with the help of Junko and Kuroko.

With the secret admirer case solved, Junko returned alone to the doll they discovered earlier, only to be surprised that an actual ghost emerged inside of it. Junko would later spend the next few days being possessed by the ghost. One particular day, the ghost girl revealed that she wanted to ask for help in investigating what happened to her and her memories, and Junko agreed to help.

Attack Against the Shokuhou Clique
While the Shokuhou clique tackled an incident involving Shokuhou Misaki's bag being taken by a lemur, Junko planned to keep her agreement with the ghost girl a private matter. However, Misaki urged Junko to tell her problems as part of her vow as clique member, and Misaki began to use her powers to help Junko make progress on the case of the ghost girl by taking a Tokiwadai student's accurate drawing of the ghost girl. A later visit by Junko to the Judgment 177 Branch Office allowed her to meet Saten Ruiko and Uiharu Kazari who agreed to help in her case.

After the clique successfully captured the lemur that stole Misaki's bag, a plan to track down the culprit by using the lemur was put in place. However, Misaki was unaware that it was a trap set by Yumiya Iruka and her accomplice. Makigami Komaki, who was on patrol nearby, responded to the incident and quickly confronted Misaki's attackers, only to be taken down by the accomplice's combat ability. Komaki managed to contact Junko during the clash, allowing her to fight the two attackers in her stead, but despite being close to defeating Iruka's accomplice, Junko was caught in a trap and helplessly watched as Misaki was taken by the two. Through the uplifting words of fellow clique member Kobayashi Satori, Junko temporarily assumed leadership of the Shokuhou clique to initiate a plan to rescue the Queen.

The ghost girl managed to locate Misaki and possess her, freeing Misaki from the effects of the "malicious Indian Poker card" used on her. She then contacted Junko, enabling her to locate Misaki within School District 10. While possessing Misaki, the ghost girl tapped into the memories of being within one of the Clone Dolly facilities, Ideal. Here, she saw Mitsuari Ayu and the Yumiya siblings Rakko and Iruka. She also saw how Misaki cured the cluster headaches Junko experienced as a result of her esper ability development. However, what baffled the ghost girl is that she did not know whose memories she was accessing.

Junko soon arrived at Misaki's location, where Iruka waited for her alone with Misaki's phone. Before a fight could happen, Iruka evaded Junko's question about her motivations and instead urged for a fight to the death to happen between them. With direct combat proving difficult, Junko switched to strategically weakening Iruka's strong points using water and she overwhelmed Iruka by overcoming the light flash she used on Misaki by using her esper ability. Iruka managed to get up again and used a "sacrificial" tactic by overloading her artificial right eye and using her esper ability to cover the entire area with light beams. Junko managed to withstand the hits from Iruka's powerful attack and quickly tended to her opponent after recovering from her wounds.