"August 21, Part 1" (八月二十一日① Hachi-gatsu Ni-jū-ichi-nichi ①?) is the 33rd chapter of the Toaru Kagaku no Railgun manga series.
The chapter opens with Mikoto riding a bus towards the Tree Diagram, arriving at the Tree Diagram Information Receival Center. She tells a member of the center's staff that she's here to get information for her summer vacation report, and is warned to stay away from the fenced off area. Mikoto pretends to agree and infiltrates this area, using her powers to bypass the security robots and climb over the wall. As she is running towards the building, she thinks about her plan to make Tree Diagram produce a false prediction to stop the Sisters being killed, which would buy her time to bankrupt the Level 6 Shift Project.
Meanwhile, Kusakabe Yumi and Kanmi Eiga are in a laboratory examining Misaka 10032, due to her complaining of chest pain (which in turn was due to Mikoto asking her to go away). Misaka 10032 asks both scientists a hypothetical question: what if they were to meet their own clone? Both respond negatively. Misaka 10032 leaves the laboratory believing that Mikoto doesn't want her to exist, walking past a black kitten and ignoring it.
In an alley, Accelerator brutally beats up some thugs who tried attacking him. He spots a Sister at the entrance of the alley (Misaka 10032, refusing to hold a kitten that Kamijou Touma is holding out to her) and is reminded of the experiment, so he begins walking towards her.
Upon entering the building, Mikoto becomes suspicious as there is nobody else present and the surfaces are covered in dust. She hacks into the computer and discovers that Tree Diagram has been destroyed.
In order of appearance:
- Misaka Mikoto
- Misaka 10032
- Kusakabe Yumi
- Kanmi Eiga
- Misaka 10032's cat (cameo)
- Kamijou Touma (cameo)
- Electromaster (Railgun-variant) - Misaka Mikoto, Level 5
- Accelerator (ability) - Accelerator, Level 5
- During Mikoto's infiltration of the Tree Diagram Information Receival Center, a report is shown, among other things, referring to the request for Tree Diagram to calculate Mikoto's panties. Mikoto however, doesn't notice this.
- In Mikoto's imagination, researcher's face is depicted with henohenomoheji. It is a face drawn by Japanese children using hiragana characters.