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For the Toaru Kagaku no Railgun S episode of the same name, see Toaru Kagaku no Railgun S Episode 14.

Promise (やくそく Yakusoku?) is the 15th episode of Toaru Kagaku no Railgun T. It was broadcast on May 22nd 2020.[1] The episode was directed and storyboarded by Sayama Kiyoko, and the screenplay written by Yasukawa Shogo.

Kouzaku, who had undergone ability development at Clone Dolly, was asked to look after Dolly, who was also in the same facility for similar treatment. One day, Kouzaku's suspicions on Dolly's life support systems led her to discover the truth behind the girl's "treatment". Dolly, an artificially-produced clone, had her life shortened because of her exposure to experiments. Kouzaku's demands to stop the experiment were futile, and soon she was separated from Dolly.

Fueled by deep rage and hatred against Academy City, she fought, swearing to take revenge, but her plan that she struggled to put into fruition once again ended in failure. What awaits ahead of her is an encounter with another girl related to Dolly, "Misaki-chan".


As a young girl, Kouzaku Mitori spent her days developing her ability at a certain facility. During this time, she developed an enthusiastic facade to the scientists who were examining her, believing that her efforts only determined her future and were not appropriately rewarded. One day, a scientist entrusted to Mitori a clumsy girl named Dolly, who suggested that the girl's stress levels would improve in the presence of a friend. Mitori was apprehensive about watching over Dolly due to her own opinions on the stranger. Eventually, she learned to interact with Dolly, enabling her to know more about the girl, notably her ongoing "treatment", the "little sisters" she hasn't seen, and her interest in sea life. In turn, Dolly became close to her; Mitori learned to pinch Dolly's nose to tease her tendency to get the scent of other people, while Dolly learned to pinch Mitori's cheeks in response as well as give her a twintail hairstyle in one occasion.

Mitori soon began to realize that the smiles she was showing to Dolly were becoming sincere. But, one day, Mitori discovered the large stitches across Dolly's body during her checkup. Another scientist explained to Mitori that Dolly needed a life support system to survive, but she remained suspicious. After using her liquid metal puppet to steal a flash drive from within the facility, she learned about Dolly's ongoing "treatment" and her status as a clone and singlehandedly tried to demand its stoppage in front of a scientist in the facility. However, her attempt instead revealed that the Board of Directors requested the experiment in the first place. Mitori desperately tried to attack the scientist, but was quickly subdued and imprisoned in a solitary confinement chamber.

An indefinite amount of time passed, and Mitori discovered that the security systems in the facility had been disabled and the entire facility had been emptied out. Upon seeing the Windowless Building, Mitori reignited her hatred against the people who were treating others as guinea pigs and began a series of assassination attempts on the Board of Directors, all leading to failure and imprisonment. In one instance, a man named Kihara Gensei entered a deal with her, allowing her to enact her revenge on Academy City after seeing the beauty in her spirit of vengeance.

Ultimately, Mitori faced yet another defeat after realizing that she was still alive despite the plan to force Misaka Mikoto into Level 6. There, Shokuhou Misaki confronts Mitori, certain that the restrained girl is "Mi-chan" from Gensei's memories. Misaki also reveals that she was supposed to take the role of "the girl who abandoned Dolly". Wanting to clarify things about her and Dolly's fate before she would be taken to the authorities, Misaki asks Mitori to come with her after disabling her restraints.

In the Judgment 177 Branch Office, Saten and Mikoto join Uiharu and Mii in celebrating Kuroko's full recovery. As Kuroko enjoys being pampered by Mikoto, Uiharu asks about her mother, who was involved in the attacks earlier. This reveals to Mikoto that her friends still had memories of previous incidents, but may have revisions as Misaki deemed necessary. Regardless, one incident remains mostly intact, and it involves Saten being snoopy regarding the Shadow Metal urban legend.

Misaki soon brings along Mitori to an unknown facility, where she talks more about Dolly and her surprisingly sharp intuition. Then, they continue inside the facility, heading towards the area where Dolly's clone, who inherited the original Dolly's memories, was stored. A tearful reunion occurred between Dolly and Mitori, with Dolly pinching Mitori's cheek and Mitori pinching Dolly's nose. This also started their first conversation after a long time apart.

Then, Dolly calls out to Misaki, who had been Dolly's companion after Mitori disappeared. Misaki apologizes for deceiving her about being "Mi-chan", for being carried away by the lie she created, and for not doing anything to expose about the truth about Dolly's experiment. Dolly instead asks a favor to Misaki: to be able to see the things in the world that she wanted to see since then.

At a certain hospital, Mikoto visits her clone who is also recovering well after the events that had happened. Misaka 10032 is disappointed for missing out on the rest of the Daihaseisai, and decides, for some reason, that a visit to the beach would make up for it, much to Mikoto's confusion.

Adapted From

Major Events





  • The unnamed researchers are voiced by Shiomi Souma, Torigoe Maaya, and Yamamoto Shōta.


Cultural References

  • Aurora, also known as northern lights (aurora borealis) or southern lights (aurora australis), are lights created when charged particles from the solar wind emitted by the sun hit the magnetic field of the earth and interact to emit light. The best place in Finland to see the Northern Lights is Lapland above the Arctic Circle.
  • Hawaii is a state of the United States of America located in Pacific Ocean. The dolphins can be seen in several places in Hawaii.
  • Machu Picchu is fifteenth century Inca citadel, located in Peru, on a mountain ridge. The llamas can be seen in Machu Picchu as well.

Differences in Adaptation

  • In the episode, food packs were given to Mitori after she gets locked up, but originally, there are none in the manga.[6]
  • Mitori's attack at the Windowless Building is anime-original, as the manga just skips it, meaning the readers has no idea on how she attacked the building.[6]
  • The scene in Judgment 177 Branch Office in the second half of the episode, where Mikoto and friends celebrate Kuroko's recovery from her injuries is anime-original.
  • The scene in the car with Misaki and Mitori on their way to retrieve Dolly's new body is anime-original.
  • Dolly's reunion with Mitori at the start has added some small details, such as Mitori pinching Dolly's nose and the latter stretching her cheeks like before, as well as Dolly clutching her stomach as the scars were there, to ensure a much more impactful reunion. The same reunion scene in the manga does not have these small details.[7]

Animation Trivia

  • Just like the previous episode, this episode starts with the OP before the episode proper, which is unusual for Railgun and by extension, Index anime adaptations.[3]
  • The scene of Mitori and Misaki from Railgun T Episode 14 is reused in this episode, albeit extended.[3]

Unanswered Questions


# Title Time Scene & Notes
Unverified Track
final phase Opening
Unverified Track Part 1
Unverified Track Part 2
Koko ni Itai Insert song, used when Mitori and Misaki finally see Dolly again
Sono Kimochi no Saki ni Mikoto checking on her "sister"'s fever[8]
nameless story Ending
Unverified Track Preview



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