"August 15, Part 4" (八月十五日④ Hachi-gatsu Jū-go-nichi ④?) is the 24th chapter of the Toaru Kagaku no Railgun manga series.
The chapter opens with the continuation of a scene in Chapter 20, where Kuroko asks Mikoto what she would do if her own clone were to appear. Mikoto answers that "Well, I think i'd feel a bit sick and want her to disappear from my sight." with a smile.
Continuing from the last chapter (Where Mikoto saw Accelerator kill Misaka 9982), Mikoto rushes towards Accelerator and attacks him, but is easily repelled. Mikoto is at first concerned, but then seeing Misaka 9982's leg on the floor, screams again and attacks him with rails. Accelerator repels the rail's towards Mikoto, which she avoids, and then Accelerator realizes this Mikoto is the original one. She shouts at him, asking him what's his motivation to participate in this program if he was so strong, to which he replies that he wants 'absolute power', a power that makes other people laugh at the thought at fighting him.
Mikoto is disgusted at his response and fires off her 'railgun' at him, which he deflects once again. He starts advancing towards Mikoto, wanting a challenge, but is stopped by other 'Sisters', who tell him that the calculation might be thrown off if he fights against Mikoto. He walks off and as soon as he leaves, Mikoto's knees give out from fear. As the 'Sisters' are given orders by the Misaka in charge, Mikoto shouts at them, asking why they are willing to participate in this program, to which they reply that they are "Lab animals, after all", ending the chapter.
Adapted from? which chapter of novel
refs to previous chapters