"Yin and Yang" is the twelfth episode of the Durarara!! anime.
Seiji Yagiri attempts to stab Mikado Ryuugamine, but Celty Sturluson protects him. Seiji demands that he get 'Celty' back, and the Black Rider swings her scythe at him, but a voice suddenly screams for her to stop. It is the redheaded girl, whom Mikado recognizes as Mika Harima. Staring at the face of the crying and screaming Mika, Celty realizes that the head on Mika's shoulders is not hers.
Upon hearing that his lover is actually Mika, Seiji stares in disbelief while Mika apologizes. In the past, Mika had fallen in love with Seiji during school entrance exams, and when she picked the lock to his apartment, she noticed a head in a jar on Seiji's table. Seiji found her inside, and though Mika promised she wouldn't tell, to protect the head, Seiji smashed her head into the wall. After her unconscious body was collected by Namie Yagiri's men, Namie persuaded her to undergo plastic surgery from a doctor who told her that her name would be Celty. However, this wasn't enough for Namie, who wanted Mika to start taking drugs to erase her memories. Celty ponders Mika's confession of a doctor who knows her name - Shinra Kishitani - and drives off to find him.
Seiji is floored and furious to find Mika is not the head of Celty. Izaya Orihara laughs and remarks that he couldn't even tell the difference, so their love must not have been very strong. Mikado admires that Seiji and Mika both took a lot of risks for each other and remarks on their similarities.
At Celty and Shinra's apartment, Celty confronts and prepares to question Shinra, but Shinra asks and answers all of her questions and reaffirms his love for her. He reveals his fear of losing Celty if she were to find her head, since it is Celty's lack of a head that allows her to act so much like a human.
Celty reveals to Shinra her fear of dying. She understands the strength of her body, but her head is defenseless, and she worries about how easily she could die if someone were to destroy her head. Shinra finds it amusing they are both getting worked up over hypothetical situations and accepts Celty's request to punch him. In response, he knocks off her helmet so he can see the shadows where her face would be, stating that he considers the punch a kiss to celebrate their marriage, earning him another jab from Celty. He hugs her and she falls on top of him, and Shinra asks if she is crying. Celty responds that he is an idiot.
Still on the street where the Dollars crowd is dispersing, Izaya observes the dwindling chaos of the meeting and is greeted by Kyouhei Kadota. Izaya asks him where the name 'Dollars' came from. Kyouhei thinks it stems from the thuggish phrase "give me all your dollars," but Izaya reveals that the real root of the name is "dala dala," meaning "to do nothing." Walker Yumasaki and Erika Karisawa arrive and exclaim about the events of the evening, and Izaya shocks them further by telling them that the Black Rider is also a member of the Dollars.
Izaya congratulates Mikado on the turnout at the Dollars meeting and warns him that all this commotion will seem normal in a few months. Mikado would have to move to another country or more underground activities to keep life exciting. Izaya quickly hides behind Mikado as a large object comes flying toward him, courtesy of Shizuo Heiwajima. Before running away, Izaya wishes Mikado a good day, calling him TarouTanaka and revealing his status as one of Mikado's fellow Chat Room users.
The next day, everything returns to normal. At Raira Academy, Masaomi Kida explains to Mikado an outsider's view of the previous night's events. Seiji tells Mika that although he does not feel any love toward her, he is reminded of Celty every time he sees her and so will continue their relationship. As Celty meets Izaya for a job, he tells her that people won't be afraid of her anymore because she no longer lives in the shadows. He advises her to call him if she needs help with Namie, but Celty doesn't want to find Namie - she just wants to be herself.
At Raira, Mikado ponders his conversation with Izaya and wonders if everything will eventually become just a part of the mundane. Seiji and Mika appear and apologize to Mikado, thanking him for all he did for them, then sit in adjacent classroom chairs. Anri realizes that she won't spend much time with Mika anymore and that most people can't understand their own heart.
In his apartment in Shinjuku, Izaya comments on Namie's willingness to throw away everything for her brother's love. He provokes her by reminding her that Nebula is planning to merge with Yagiri Pharmaceuticals, which would prove problematic should they receive wind of the Mika incident. It is revealed that he was the one texting and calling Mika using the name 'Nakura' and advising her on how to stay with Seiji. He moves several pieces on his mixed gameboard and regrets the inability of the kings to directly fight one another. He notes his own skepticism and desire for the afterlife.
According to Izaya, Dullahans are Valkyries fallen to earth. Celty's head is alive but asleep because she is waiting to wake up during a war to guide her warrior to Valhalla - and Izaya wishes to be that warrior. He will start a war only he can win, because although he doesn't care whether he goes to heaven or hell so long as he exists, he would prefer heaven. He then holds Celty's head in his hands and muses that Celty will never expect to look for her head within her own gang - the Dollars.
The day after the Dollars meeting, TarouTanaka states that he did not get enough sleep the previous night and wonders to Setton if Kanra will come on. Setton has to go almost immediately, however, and the chatroom is left empty.
- The events in this episode are a direct continuation of the events in the previous episode
- To Mika's advice texts from 'Nakura'
- To Izaya's phone conversation while Celty and Mikado talked under the bridge
- To Kyouhei's gang chasing the cleaning van that caused a rock to hit their van
- To Namie's men taking Mika's body out of Seiji's apartment
- To Shinra asking Celty to marry him
In order of appearance, excluding the opening song:
- The company Nebula that is mentioned to be buying out Yagiri Pharmaceuticals is the same company in Baccano! that manages immortal-related incidents. Both Baccano! and Durarara!! are works in the Naritaverse.
Izaya (to Seiji): "Well, you couldn't even tell the difference between the genuine article and the fake. Guess your love wasn't that strong after all. Sucks to be you."
Mikado (to Seiji and Mika): "Um, I have to say, the fact that you were willing to risk your life to get her back is pretty admirable. And it turns out that I was actually wrong about Mika. Some of the things she does may be strange, but I really don't think she's a stalker. I mean, you risked your life to save Seiji. I don't think someone would do that if they were only in it for themselves. And even though he tried to kill you, you still loved him. That's amazing, in some ways. So then, I guess, you and Seiji, you're a lot alike."
Celty (to Shinra): "I'm scared, too. I'm scared of dying."
Izaya: "Human beings defy imagination."
Izaya (to Mikado): "Remember: I know you came here to Tokyo hoping to escape the hum-drum, but in about six months this will all seem pretty ordinary to you. At that rate, you'll have to move to another country to keep things exciting. Or start looking for things that are a little more 'underground.' But, I'd be willing to bet that you would get bored of that in just a few days as well. The only way to truly escape the mundane is for you to constantly be evolving. Whether you choose to aim high or aim low, enjoy each day for what it is."
Celty: "I have no idea where Namie Yagiri went, but I don't care. I'm me: and that's enough. My days were always pretty uncomplicated, not too full of hope or despair. And they're still like that. It's just that now, I find them incredibly satisfying. Here I am, and there you are. If you can find redemption in me, then I can do the same for you."
Celty: "The young boy is still pondering his conversation with Izaya Orihara. Can a person truly have a life that's always new? Always full of excitement and possibility? Or is it just a matter of time before that, too, becomes part of the everyday?"
Izaya: "Hey Namie, why don't we all go to Heaven?"