Yokohama Disturbance III is the twenty-first episode of the Mahouka Koukou no Rettousei anime.
The Magic Thesis Competition team meets continued success in developing their project, though Erika, Mikihiko, and Leo apprehend a fleeing student, Chiaki Hirakawa, who is revealed to be working as a spy against the First High team. Chiaki admits to working against Tatsuya personally, passionately believing that he is responsible for Kobayakawa's accident during the Mirage Bat event of the Nine Schools Competition. Erika and Leo take a day off together to train Leo how to use lethal magic, with Erika believing that the conflict will more likely escalate to kill or be killed. Mikihiko chases after an embarrassed Mizuki, unintentionally bumping into an ominous figure dressed in a First High student uniform.
October twentieth. The school is abuzz with activity as preparations for the Thesis Competition get into full swing and a number of students are working to assist.
A large number of students have gathered to watch Suzune testing one of the presntation devices with help from Kei and Tatsuya. At Kei’s signal, Tatsuya shuts down the device, concluding the successful test which elates the crowd. One of the guards, Mibu Sayaka notices a girl using a device in the crowd and rushes into action, surprising her partner Kirihara Takeaki. The girl realises and makes a run for it and Sayaka gives chase, which is noticed by Erika. Chased by Sayaka, the girl runs until she is out of breath and has to stop. Sayaka introduces herself, forcing the girl to introduce herself, revealing she’s Hirakawa Chiaki. Takeaki, Erika and Leo catch up, with Takeaki immediately recognising the Hirakawa family name. Sayaka asks about the device Chiaki has, stating it’s a wireless password breaker, telling Chiaki it’s pointless to hide it as she herself has worked with spies before. Sayaka tries to convince Chiaki to cut ties with them, not wanting to go down the same path she did but Chiaki can’t be reasoned with. Realising this Sayaka signals Takeaki and they approach to take Chiaki in. Chiaki pulls a flash grenade and only Erika reacts in time, leaving the other two stunned. Chiaki then fires a dartgun hidden in her sleeve at Sayaka, but Erika blocks it with a twig. The dart fired releases Teargas and Erika pushes Sayaka out of the way but Takeaki is left choking. Chiaki backs off while keeping the dart gun trained on Erika so she can’t make a move. Leo charges in and tackles Chiaki before she can react and fire again, the blow knocking her unconscious. Leo realises he knocked Chiaki out and is left wondering if he over did it.
In the Nurse’s Office, Chiyoda Kanon scolds Sayaka and Takeaki for going overboard. She asks Asuka Satomi, the nurse, how Chiaki is and Asuka advises she’ll be fine and will wake up soon. Kanon asks her to message her when Chiaki wakes up as she herself needs to return to her guard duty. Asuka agrees but stakes she has no combat abilities so won’t be held responsible if Chiaki escapes. Kanon returns to her post to find Sekimoto Isao making a scene, shouting at Erika and Leo. Kanon asks Tatsuya what happened, and he tells her that Sekimoto took issue with Erika and Leo being there. Kanon goes over and asks what’s going on. Sekimoto tells her he’s telling the Course Two students not to wonder around. Kanon states for the record that there is no issue with first years observing and if there is, then the actual guard detail will handle it. When Sekimoto tries to use his status as a Public Morals Committee member, Kanon states it’s been handled by another group and asks him to leave it to them. Kanon then asks Erika and Leo to leave due to the incident earlier with Chiaki. Erika and Leo head home. Kanon then gets a message and heads of and Kei follows her. Alone, Sekimoto sees the terminal Kei put down before he ran after Kanon and approaches it, but Suzune turns it off and comments she though he had no interest in this sort of practical theme. Sekimoto then leaves.
Leo and Erika are walking home when Erika asks if Leo has some free time. When he tells her he’s free, she asks him to come with her. Kanon and Kei arrive at the Nurse’s Office to find Asuka pinning Chiaki to the floor. Kanon asks Asuka to sit Chiaki down so they can talk. Kanon begins by stating Chiaki was reckless the other day as well, referring to the incident with the scooter. Kanon asks why Chiaki tried to steal the data, and Chiaki states she was trying to rewrite the program to disable the device for the presentation instead. Kanon asks if she wanted the presentation to fail, and Chiaki admits ‘that guy’ would be able to handle it but maybe he’d at least panic a little. Kanon is shocked Chiaki did something that could get her expelled out of spite. Chiaki says she doesn’t care if it means getting one over ‘that guy’ and starts crying. Kei steps in an asks if Chiaki is Koharu’s younger sister and that she blames Tatsuya for what happened to her sister. Chiaki admits she does, claiming Tatsuya left Kobayakawa Keiko for dead and her sister felt responsible. Kei calmly states that if Tatsuya is in any way responsible for that incident, then the entire engineering team is equally at fault for not seeing the sabotage. Chiaki gets a crazed look and denies what Kei said, saying if her sister couldn’t tell, then none of them could have and that only Tatsuya saw it due to who he is and that even ‘that man’ agrees. Kanon silently reacts to her words. Asuka steps in and ends the conversation there, saying she’ll send Chiaki to the Magic University Affiliated Hospital for the night and asks them to continue the questioning tomorrow.
Leo and Erika are in a commuter, sitting in silence when Erika suddenly asks if he thinks it’s too simple. Leo is unsure what she means, and Erika tells him it’s not over, thinking Chiaki is a decoy. Leo asks if she wants him to play detective and smoke out the real culprit. Erika says they should leave the thinking to Tatsuya, and Leo asks if they’ll be bodyguards then. Erika states she thinks they’ll be counterattacking rather than defending, but there is something lacking in that regard. Erika tells Leo she thinks his latent skills as a foot soldier are first-class but he’s lacking a trump card, the kind of move that’s sure to kill an opponent. Leo asks if she has one and she confirms she does. Leo then admits we lacks a technique meant to kill the opponent. Erika says it doesn’t have to be them, but if Leo is serious about getting involved, then he needs to be ready to kill or be killed. Erika asks if Leo is prepared for that, and when he confirms that he is, she agrees to teach him one of the Chiba Family’s secret sword techniques, the Antlion. It’s very late when the Shiba siblings head home from school with their friends. They are joined by Kanon and Kei who tell him about Chiaki. Honoka is angry at Chiaki’s unjustified grudge whilst Shizuku ponders whether Chiaki is simply taking it out on Tatsuya. Mizuki comments that Chiaki really loves her sister and Mikihiko nods his head in agreement. Tatsuya comments they can just ignore the situation if that’s the case. Kanon refutes that he’s the one being targeted, and Kei says he thinks that they should get her sister Koharu to talk to her. Tatsuya tells them not to involve Koharu as she’s not responsible. Kanon annoys Miyuki by commenting that Tatsuya does have a nice side, but Tatsuya simply says that involving Koharu could escalate it and besides, Chiaki isn’t the only one who has been skulking around.
Chen Xiangshan, accompanied by Lu Ganghu, meets with Zhou Gongjin and reports that Chiaki was caught. Zhou explains Chiaki knows nothing of them so her getting caught is not a threat. Chen comments he’s impressed Zhou could get her to collaborate and Zhou simply explains that people her age are easy to manipulate. Chen says he’s relying on Zhou to ensure nothing unexpected happens and Zhou assures him he will appraise the situation.
At First High, the Shiba siblings are having lunch with their friends when Honoka asks why Leo and Erika are missing. Tatsuya tells her that they are both off today. Honoka gets excited, asking if they are off together which Tatsuya confirms. The group speculate whether they might actually become a couple though Mikihiko comments he’s not noticed anything. Tatsuya speculates Erika is likely running Leo into the ground right now. At the same time, Leo is in training gear and accidentally walks in on Erika while she is in only a towel after a shower.
Later, at the Chiba Dojo, Erika continues training Leo with the sword, bickering like usual. Leo is struggling to stop wrinkles forming on the cloth he’s holding. Erika comments he could do it with the cloak in the Nine Schools Competition match and Leo explains that small wrinkles didn’t affect its function as a shield and that it had an auxiliary spell incorporated into it. Erika says this cloth does too and wonders whether they should ask Tatsuya. Leo refutes the idea, saying bothering Tatsuya would defy the point and gets up to try again and resumes the training.
October twenty-second. While work is still underway for the Thesis Competition, Juumonji Katsuto is training with the security team to prepare them for the competition. Watching though a monitor with Mari, Mayumi is worried that the training may break their confidence instead. Mari comments it’s likely because Katsuto is in charge overall. With seven already down, they wonder who is left when Mari notices Mikihiko. I the forest, Mikihiko is wondering if he jumped the gun by agreeing to participate. Mikihiko realsies he’s been detected and waits for Katsuto to approach. When Katsuto is in position, Mikihiko unleased his trap magic and collapses the ground under Katsuto and makes a break for it. When the dust settles, Katsuto is smiling while standing on a barrier he created, clearly impressed.
After the training, Mikihiko is chatting with Sawaki Midori. when the girls arrive with food. Mikihiko Is invited to eat with them too. Mizuki brings Mikihiko his food and one of the other girls brings Mizuki her meal and tells her to take a break too. The pair eat in an awkward silence until Mizuki asks if Mikihiko wants more tea. She accidentally catches his hand and the pair get even more embarrassed, the awkward first-love atmosphere they are generating being noticed by everyone in the room. Mizuki tries to get up but stumbles. Mikihiko catches her but accidentally grabs one of her breasts in doing so. When they realise, both get incredibly flustered and as Mikihiko apologises, Mizuki tries to run away and trips, flashing the room. This is too much for her and she ends up fleeing the room in tears. One of the girls angrily shouts at Mikihiko for spacing out and tells him to go after Mizuki. As Mikihiko chases Mizuki to apologise be accidentally bumps into another student who seems to be skulking around.