Death's End

Engineer Yun Tianming is in love with Cheng Xin, who does not reciprocate romantically, but does love him as a friend, making him a quasi-love interest. Yun Tianming is mostly absent from the narrative; however, he eventually comes to influence humanity across centuries.

Yun Tianming begins the novel as a terminally ill patient suffering from unrequited love and an inability to connect with other people. Rather than electing euthanasia, he chooses to donate his brain to the problem launched via the Staircase Program—but only out of love for Cheng Xin, and after refusing to pledge allegiance to humanity: “’I will not take the oath. In this world, I feel like a stranger. I’ve never experienced much joy or happiness, and didn’t receive much love” (94). This thorough alienation makes him the perfect spy to use against the Trisolarans, who ostensibly are more likely to catch his probe and reconstitute his body because they don’t see him as Earth’s ally. This pre-space Yun Tianming is defined by his isolation and commitment to Cheng Xin, making him insecure and at times unsure of what he wants or needs.

When the capsule containing Yun Tianming’s brain goes off course, Cheng Xin believes that he is lost in space. It is a shock, when centuries later the Trisolarans reveal that they have him and that he wishes to speak with her. The Yun Tianming Cheng Xin meets has changed into someone more mature, healthier, and happier. This new Yun Tianming, whose commitment to Cheng Xin remains constant, makes her more open to romantic reciprocation: “Cheng Xin’s heart quaked. Yes he had always been with her, observing her life through the sophons. [...] If she had known earlier that this man who loved her had crossed the light-years to keep watch over her, she would have been comforted” (307). Not only has Yun Tianming developed better interpersonal skills, but his time being embedded in an enemy fleet has also allowed him the professional success that he never achieved on Earth: He learns many aspects of theoretical astrophysics and technology from the Trisolarans and encodes his new knowledge in a message that can get past their intense censorship—fables that he hopes Cheng Xin and other people can decipher. Yun Tianming wants not only to save humanity with his tales, but also to be with Cheng Xin when his life ends. Their would-be love story does not get a fairytale ending, however: Just as they are poised to live out their days on the star he gifted her, Cheng Xin and Yun Tianming are separated by millennia when her ship gets caught in a zero-light-speed trap.

Sophon is an AI android remotely controlled by the Trisolaran fleet; she is the only physical manifestation of the Trisolarans humanity has access to. Sophon’s role throughout Death’s End changes; because she is controlled by Trisolaris, she has limited free will and is primarily serving a purpose others have assigned. At first, she appears to be an ally to Cheng Xin and humanity—a diplomat between the two worlds. When Luo Ji becomes unpopular as Swordholder, Sophon encourages Cheng Xin to step into the role. However, this polite version of Sophon quickly turns out to be a ruse: After the Dark Forest Deterrence ends, Sophon becomes an antagonist, taking on the role of a conqueror—directing the human resettlement into reservations on Australia to prepare for the arrival of the Trisolarans. This enemy Sophon is described through similes that show how Sophon’s precision and elegance can be both welcoming and brutal: “Around her neck was the black scarf of a ninja, and on her back was strapped a long katana [...] Her postures and movements were still soft and gentle like water, but now they were also suffused with a glamorous air of killing and death, like a pliant but fatal noose” (187). At the end of the novel, after Trisolaris has been destroyed, Sophon ceases to be antagonistic and becomes a guide for Cheng Xin and Guan Yifan: “She had all sorts of weapons and survival gear strapped to her body, the most prominent being the katana on her back. ‘Don’t worry,’ she said to her two human friends. ‘As long as I’m alive, no harm will come to you’” (602). Here, the weapons of a tyrant become the tools of a protector—another role Sophon slips into easily because she has little inner life, and instead has been designed to follow directions and be a mouthpiece to another civilization.

Government agent Thomas Wade is Cheng Xin’s foil in the novel. Both often work on the same technologies—the Trisolaran probe, light-speed travel—and aspire to the same positions, such as Swordholder, but their opposing perspectives pit them against each other. Wade is a pragmatic, brutal man guided by the idea that the end of human survival justifies any means used to achieve it. This is at odds with Cheng Xin’s empathetic approach to the world. When they meet working on the Staircase Project, Wade is rabid about the need for progress: “He dropped his habitual indifferent tone and screamed like a crazed wild animal. ‘We’re going to advance! Advance! We’ll stop at nothing to advance!’” (70). This over-the-top commitment to success at any expense makes him an ideal Swordholder candidate: Unlike Cheng Xin, he is credibly willing to destroy Earth if it means also destroying Trisolaris. Whereas Wade is willing to reveal the location of both Earth and Trisolaris, Cheng Xin cannot bring herself to knowingly hurt others, making her a weak and ineffective Swordholder. Knowing this leads Wade to attempt to murder Cheng Xin to solidify his hold on the Swordholder position.

After the destruction of Trisolaris, Wade continues his fixation on humanity’s survival above all—this time by expanding humanity’s place in the universe. This leads him to crave the authoritarian power to circumvent laws such as the ban on light-speed travel research. Though Cheng Xin disagrees with his methods, she does work with him on curvature propulsion, seeing in it the promise of countering a dark forest strike. Because Wade has been so rigid in his beliefs, it comes as a surprise that he honors his promise to Cheng Xin to relinquishes control of the project if she finds that his actions may hurt others. Rather than starting a war with the other Bunker World cities, “Wade gestured for the self-defense force to leave. They departed noiselessly, and the hall brightened as though a dark cloud had dissipated. [...] He closed the dome, turned to Cheng Xin, and smiled. ‘You see, I’ve kept my promise, little girl’” (460). Ironically, it is Wade’s reluctance to deviate from his beliefs that ends up saving what little humanity manages to escape the collapse of the Solar System into two dimensions: His light-speed enabled ship conveys Cheng Xin and AA away from Pluto to safety.

Astrophysicist AA is Cheng Xin’s friend, confidante, and sidekick. When Cheng Xin wakes from her first hibernation, AA becomes her guide to the changed human society, helping Cheng Xin acclimate. The cultural differences created by them having grown up in different times also make AA a foil to Cheng Xin: Whereas Cheng Xin has an idealistic sense of duty to humanity, AA is guided by a more realistic need for survival. For example, in the aftermath of a false dark forest strike warning, AA wants to join the escaping spaceships but Cheng Xin refuses, unwilling to harm the people on the ground that would be burned by the launch. In response, AA points out that in death, morality no longer matters: “Can you tell which ones are honorable and which ones despicable in that mess?” (394), criticizing Cheng Xin’s commitment to honor by arguing that ideals don’t matter to the indifferent universe. Despite their disagreement, however, AA follows Cheng Xin’s instructions.

Though AA is loyal to Cheng Xin, following her through time and space, she is an individual with an independent mind. When Cheng Xin and Guan Yifan are trapped in the black domain around Cheng Xin’s star, Yun Tianming and AA live out their lives together rather than waiting in the mini-universe Yun Tianming has brought. Though she is devastated, Cheng Xin recognizes why AA would choose this: “AA always cared more than me about the world around her. I don’t think she would have been interested in a new universe tens of billions of years later” (587). In this, AA continues to be a foil for Cheng Xin—she gets to have the life with Yun Tianming that Cheng Xin wants. Ultimately, Cheng Xin respects AA’s decision, accepting that AA and Yun Tianming are their own people rather than merely bit players in Cheng Xin’s life.

Luo Ji is an obscure scientist who is named one of the Wallfacers—people given enormous resources to implement any secret plan against the Trisolarans—because he is the only person targeted for assassination by Trisolaris. As Wallfacer, Luo Ji discovers the dark forest theory: that the universe is full of advanced civilizations that annihilate others immediately on locating them. As a result, he develops the Dark Forest Deterrence—keeping Trisolaris at bay under threat of broadcasting their location and thus ensuring the destruction of both Trisolaris and Earth. Luo Ji becomes the first Swordholder, or the only person with the power to turn on the location broadcast—and thus, one of the most consequential humans on Earth. As Swordholder, Luo Ji is believably capable of dooming Earth to fend off the Trisolarans: “[H]is gaze was endowed with the chill of the underworld and the heaviness of the rocks above him, endowed with the determination to sacrifice everything. The gaze made the enemy’s heart palpitate and forced them to give up any ill-considered impulse” (171-72). This willingness to risk the safety of humanity to preserve its freedom makes Luo Ji another foil to Cheng Xin, who succeeds him as Swordholder. Unlike Cheng Xin, Luo Ji does not view the Trisolaran Crisis as an opportunity for collaboration; however, unlike Thomas Wade, Luo Ji does not believe that the constant threat of Trisolaris should lead to relentless technological progress. Nevertheless, Luo Ji is the person whose experience most closely resembles Cheng Xin’s.

On Pluto, without the burdens of the Wallfacer and Swordholder positions, Luo Ji turns into his old self: “The stately Swordholder was gone. They didn’t know that the cynical, playful Luo Ji in front of them now was a return to the Luo Ji from four centuries ago, before he had become a Wallfacer” (504). Like Cheng Xin, Luo Ji spends centuries under the weight of immense responsibility. Without it, he can let go of his stoicism and instead accept the fate of humanity to die in the two-dimensional dark forest strike. Cheng Xin and AA are shocked to encounter this Luo Ji, who is committed to the task of preserving human artifacts rather than humans themselves. However, Luo Ji reveals some of the qualities that made him a successful Swordholder when he commands Cheng Xin and AA to escape the two-dimensional collapse on the only light-speed ship humans developed.