heng (Yi's sister)

Heng is similar in appearance to Yi, as they are siblings. She shares the same features as her brother—pointed ears, cream-colored fur, and almond-shaped eyes—but there are still some key differences between them. She tends to show more emotions and facial expressions than her stoic brother, with two pink, blush-like patches appearing on her cheeks whenever she is excited, embarrassed, or annoyed. Heng also seems to have slightly longer eyelashes and is much smaller in appearance compared to Yi.

Unlike Yi, Heng's eyes have visible, wine-red irises. She also has long hair, a small, visible mouth, and no strands of hair framing her face. Her attire consists of a black and teal Hanfu (traditional Han Chinese clothing), which is a shirt with wide sleeves and a long, black skirt. In some flashbacks, she is also seen holding a flute.

As a child, she wore a teal cheongsam (traditional Manchu-Chinese clothing), and her hair was also noticeably shorter.

History
Five hundred years ago, Heng was born in the Xia Kingdom to two anonymous parents and his older brother, Yi. Heng and Yi once shared a very close bond. Although Heng didn't truly understand science, he was always by Yi's side.

No one knew it, but Heng had a strong connection to the Fusang Tree/Primordial Roots, being able to hear its voice. She also conversed with the tree regularly when she was a child. But Yi thought she had heard the wrong things because of her bias toward scientific evidence.

One day, during one of Yi's failed experiments developing the Mystic Nymph, Heng was protected by Yi, who sacrificed himself for her. Devastated by Yi's death, Heng wept, which prompted the Primordial Roots to revive Yi from the dead. However, as they grew older, Heng and Yi's philosophies diverged more and more, especially after their parents passed away. While Heng believed that all Solarians should respect the cycle of nature and accept returning to Earth once their lives ended, Yi disagreed and declared that scientific advancements were more important for the benefit of Solarian society. Eventually, the brothers' relationship soured due to Yi's stubbornness in seeking a solution for the council, which had promised society that they would research and find a cure for the Tianhuo virus. This prompted his older brother to impulsively leave Heng alone after he insisted on his desire to remain in Penglai. Despite the consequences, Heng had never forgotten Yi and only wanted her to live well.

Heng was described to be naive and eccentric. She was someone who believed that everyone should respect in the natural cycle of life and death. Despite her naïveté, Heng was gentle, understanding and compassionate in nature. This trait of hers was best shown in her relationship with Yi. Although she didn't really understand science, she was still supportive of him and even after their fallout, she never held any anger or grudges against her brother, instead wishing him to live well. She was curious in nature and was always asking Yi questions about things, which he patiently answered and also had a somewhat stubborn, childish and playful side to her, as seen when she spoke at Yi calling the Mystic Nymph "Azure flyer", saying to him that "It's Mystic Nymph! You said you'd let me choose the name!".

Her stubbornness is also what eventually caused a rift in her and Yi's relationship, in some aspects. While Yi believed in science and its benefits for the Solarians, Heng stuck to her ideal of having the Solarians experience life and death the natural way and remained behind in Penglai, even when Yi left her and traveled to New Kunlun.