"The Battle Begins" (開戦 Kaisen?) is the 50th chapter of the Toaru Kagaku no Railgun manga series.
Kongou Mitsuko continues her solo investigation on the disappearance of Misaka Mikoto's "sister" (i.e., Misaka 10032). As she traces the last steps of Mikoto's "sister", she tries to gather the information she had, and wonders why Shokuhou Misaki is interested with taking an esper whose powers are weaker than the fifth-rank Level 5. She soon arrives at an alleyway where 10032 was taken, and upon finding the Gekota mask that Mikoto likes, she hears the sounds of dogs barking elsewhere. Upon following the barking sounds, she sees two stray dogs surrounding a small black cat. Mitsuko assumed that the dogs are bullying the cat, so she tries to shoo them away, although Mitsuko ends up being chased by the dogs.
After a long chase, Mitsuko manages to lose the dogs, although she ended up tired because of this. Now, Mitsuko finds herself with a stray cat that needs its owner, so she decides to look for a member of Judgment to give the cat to. In her search for someone from Judgment, she stumbles upon her friend Wannai Kinuho. Kinuho recognises the cat as the one entrusted to her by Mikoto's "sister". Meanwhile, Mitsuko tries to explain what is going on, and although Wannai doesn't quite grasp the situation, she decides to keep the cat while she looks for a Psychometrist friend who can help out.
Meanwhile, a robotic dog is seen roaming District 7. It turns out that it is under Baba's control, and he is using it to scour some clues on what is going on outside. There, he catches the conversation between Mitsuko and Wannai. His attention is shifted to their small chat, and the word "sister".
Wannai soon discovers that she left her phone back in the School Garden's lockers and decides to look for it first. Meanwhile, the cat remains in Mitsuko's care as she decides to continue looking for clues. While she fantasises about becoming a hero in the eyes of Mikoto, a young boy named Baba Yoshio approaches her. He requests for a private talk about Misaka Mikoto's sister. Nearby, Saten Ruiko visits a souvenir shop and finds a limited-edition Gekota keychain for the Daihasei Festival. She thinks that someone would be interested in having one — or in fact, already knows about this — but for some reason, she can't pinpoint who that particular someone is. Then, as she tries to think who that person is, she sees Mitsuko with someone unfamiliar.
Baba is somewhat curious if Misaka's sister is in fact her true sister or someone else entirely. He decides to drop that topic and tells Mitsuko that he is here to shelter Mikoto's sister, and he wanted to get some information about her. Mitsuko is hesitant to work with Baba, so he decides to obtain the information from her... by force. Mitsuko soon finds herself surrounded by more than ten of Baba's robotic dogs. As she asks the cat on her hands to seek refuge, she faces the robot army on her own. Mitsuko soon thinks that holding back the information she has was a good decision as she was very suspicious of Baba from the start, although she is disappointed that she cannot use him to get information on Shokuhou Misaki. With no other options, she prepares to fight.
Elsewhere, Misaka Mikoto is stuck mingling with Misaki's clique and is desperate in looking for a way to get away from them. Soon, she gets her chance when a girl lets go of her balloon; using her powers, she reaches an overpass where trains travel along and catches the balloon just in time to hitch a ride on the train. Mikoto manages to get away from the range of the telepath who is among her companions earlier, but two Teleporters from the same group get to her in no time, much to Mikoto's disappointment.
Mitsuko struggles to avoid the relentless assault by Baba's robots. Because of the lack of nearby objects to use, her Aero Hand ability appears to be ineffective on the current battlefield, which is completely flat. Baba confidently requests Mitsuko to back down and cooperate with him. However, an enormous shockwave suddenly whips through Baba's robotic army, tossing them into the air. As Mitsuko prepares a counterattack, she tells Baba that his analysis of her ability was insufficient. One, she can use her abilities even on the ground; and two, her output can launch a radio tower into the stratosphere using multiple ejection points. At that moment, Baba thinks that he has severely underestimated Mitsuko's damage output. However, upon glancing at the cat Mitsuko has with her, Baba appears to have discovered his trump card. Meanwhile, Wannai, joined by her friend Awatsuki Maaya, finally finds their Psychometrist classmate, although Mitsuko is no longer there. Saten stumbles upon them and Wannai decides to ask if she has seen Mitsuko. Ruiko has seen Mitsuko, but she does not know that she is currently facing a battle on her own... and that she has just been defeated.
As a mosquito robot leaves Mitsuko's motionless body, Baba gloats about his victory, which he achieved by targeting the cat with Mitsuko and attacking using his robotic mosquito, which he deems as an expensive yet effective unit in battle. Currently, Mitsuko cannot control her body due to the effect of being bitten by Baba's mosquito, and he tells her that Misaka Mikoto must be a horrible person for making someone do this for her. Mitsuko tries to defend Mikoto despite her condition, but she is helpless against Baba's attacks against her. Until the last moment, Mitsuko keeps her arms around Misaka's cat. Baba decides to stop attacking Mitsuko upon remembering that he needs her alive and orders one of his dogs to retrieve her. However, Maaya and Kinuho arrive at the scene, who both learned of Mitsuko's whereabouts with the help of Saten, who also joins them. As Saten protests about what Baba did to Mitsuko, Baba taunts the girls and tell them about Mitsuko being second rate because of following the requests of other people. Although powerless, Saten becomes angry. However, her anger cannot compare to the feelings that Awatsuki Maaya and Wannai Kinuho are feeling at the moment. Kinuho and Maaya ask Saten to watch over Mitsuko and the cat while the two of them prepare to fight Baba.
By order of appearance:
- Kongou Mitsuko
- Misaka 10032's cat
- Wannai Kinuho
- Baba Yoshio
- Saten Ruiko
- Misaka Mikoto
- Hokaze Junko (cameo, unnamed)
- Awatsuki Maaya
- Animal-type Psychometrist from Tokiwadai (unnamed)
- (by Kongou Mitsuko) "There is nothing I cannot blow away!!!" — to Baba, as she shows her Aero Hand ability.