Jian

The Jian [鹣], also known as birds that fly together [比翼鳥], are mythical birds that possess only one eye and one wing. These creatures are born imperfect, and they need to lean against each other and act as one in order to be able to fly. Their mutual dependence is eternal, lasting through death and rebirth.

Origins
The Jian originates from Chinese mythology and its dependence on joining in pairs symbolizes the bond between a husband and wife.

Overview
The mythology of the Jian seems to be the catalyst for the ideology of the dystopian environment in which the remnants of humanity live in. APE educated the general public with propaganda on the Jian, such as bird signs on badges, monuments, military craft, and clothing. The parasites wear uniforms with an embroidered bird shape.

APE takes inspiration from the male-female pairing of the mythology by encouraging adults to follow the previous human civilization custom in men and women living together. However, the Old Woman mentions she and her partner, whom she seems to lack sharing an interpersonal relationship with, are simply following the custom and lead separate lives from each other. APE specifically encourages male-female pairing in the parasite program as a necessary way for the parasites to operate the FRANXX and fight the Klaxosaurs. However, APE deliberately leaves out the symbolic meaning of the pairing because any knowledge on emotions and intimacy is banned and punishments will be harsh, as they are concerned the parasites will become rebellious and lose interest in their priorities should they develop sentimentality.

Zero Two is very knowledgeable of the Jian. She finds them to be incomplete creatures but their way of life to be profoundly beautiful. This, along with her obsession with finding her long-lost darling, she compares her goal to flying high in the sky to reach it like the Jian. Hiro read about the Jian in a book a long time ago but finds them to be pitiful creatures for not being able to fly without a partner. However, after meeting Zero Two, his opinion on the Jian changes and he shares her perspective on the Jian.

Before they died, Hiro and Zero Two ‘became one’ via Strelizia and Zero Two declares they, as a pair who lean on each other to fly together, are truly the Jian.

In the ten-year time skip, the Jian continued to have an influence on the parasites’ lives. All the children of the former parasites have a bird embroidered on the scarves of their school uniforms. The final page of Zero Two’s picture book, The Beast and the Prince, was drawn with a colourful bird as a symbol of her and Hiro being together in death and rebirth, as they would later be reincarnated. The book also had a print of a bird on the last page with the scripture “For a pair of birds”.

Trivia

 * In the second opening sequence, one wing bursts from Zero Two's back when she sits on the klaxosaur hand. This represents her and her relationship with Hiro. Like the Jian, alone, they're unable to fly. However, when they lean on each other to support each other, they can fly freely.
 * Its wings are a set that represents their perfection in their togetherness. There are two designs that symbolize each lover: PI (right wing) and IOTA (left wing).
 * Ironically, IOTA is Zero Two’s former code name when she was in the 9’s.
 * As Squad 13 remembers Hiro and Zero Two under a cherry blossom tree, a bird flies from the tree and into the sky, symbolizing how not only have Hiro and Zero Two found their wings in each other, but the others have found their wings by leaning on one another, allowing them to form new bonds and reach adulthood in the freedom they achieved.