Mei is a major supporting character who resides on the mysterious island of Kotaku. She is originally a Tensen, a high-ranking being of god-like power, and is among the oldest of her kind, having been created roughly one thousand years before the main events of the story. She was the first Tensen created by Rien from the Tao of a puppet, though she was initially led to believe her creator was Jofuku, Rien’s husband. For a long time, she served as Jofuku’s disciple, helping to nurture and train six younger Tensen in the ways of Tao as part of research into immortality.

In terms of appearance, Mei is initially encountered as a small, shy child with long hair styled in two braided Chinese-style buns. She has golden or pink eyes and typically wears a red, long-sleeved robe, walking barefoot. However, her childlike form is not her original one. After defying the leader Rien, her plant ovule was broken as punishment, which reduced her body to that of a child and left a prominent scar-like mark running down her back. Her physical appearance is directly tied to her use of Tao; when she unleashes her power, her body matures, first to a stature similar to a young adult and eventually back to her original adult form.

Mei’s personality is defined by her shy, quiet, and innocent nature. She is easily frightened by aggressive or intimidating behavior, as seen when she first encounters the protagonist Gabimaru and cries due to his threatening interrogation tactics. Despite her timid demeanor, she is deeply kind, caring, and accepting of others, particularly once she recognizes their good qualities. Unlike the other Tensen, who view humans as lower life forms or mere resources, Mei holds no such prejudice and is willing to help the human survivors escape the island. She possesses a strong moral compass, believing that the cruel research and sacrifices inflicted upon the Hōko by Rien must be stopped. Her innocence contrasts sharply with the dark history she carries, having been sentenced to engage in Bōchū Jutsu with the Dōshi as part of her punishment, which she views with understandable terror.

Mei’s role in the story is that of a crucial ally and guide to the human vanguard party, particularly to Gabimaru and the Yamada Asaemon Sagiri. After being banished from the main Tensen palace of Hōrai, she was found and raised by a kind, tree-like creature named Hōko, who acts as her father figure. The two live in an abandoned village, hiding from Lord Tensen. When Gabimaru’s group arrives, she becomes instrumental in their survival, providing vital information about the island, the nature of the Elixir of Life, and, most importantly, the concept of Tao. She teaches the humans how to sense and utilize their own Tao, which is the source of all special abilities on the island, explaining that strength derives from accepting one’s own weakness. Her knowledge and unique abilities frequently save the group in dire situations.

Her key relationships are central to her character development. Her bond with Hōko is a deeply emotional one; he sacrifices his remaining Tao to restore her when she is on the verge of dying from Arborification, a process where her body turns into a tree due to power usage, and she honors his final wish. Her relationship with Gabimaru evolves significantly over time. Initially terrified of him, she grows to trust him after he shows her respect by telling her she does not need to hide the scar on her back. She later saves his life multiple times, and he in turn becomes fiercely protective of her, seeing it as his duty to repay her for her kindness and to prevent the Dōshi from capturing her for their training. Mei comes to see Gabimaru as a source of courage, while Gabimaru finds in her a motivation to retain his humanity.

Mei undergoes significant development and physical change throughout the narrative. Her use of Tao, while powerful, accelerates a process known as Arborification, which causes her limbs to turn into tree matter and threatens her life because she has a broken tanden. She is forced to mature quickly, both physically and emotionally, making difficult decisions to protect her friends. In her ultimate transformed state, known as Kishikai, she resembles a gigantic moth with large, petal-like wings shaped like plum blossoms, possessing feathery antennae and vines emerging from her body. Through the course of her journey, she experiences being reduced to a child, growing into a woman, and ultimately reverting to her child form again, all while grappling with her identity as a Tensen who rejects her creator’s methods. In the distant epilogue, she is shown to have survived the events of the story and continues to exist in the modern era.

Her notable abilities are rooted entirely in her mastery of Tao. As a Tensen, she possesses regeneration powers, though these are not as potent as some of her former peers. Her primary power involves the manipulation of Tao to perform incredible feats, such as creating massive craters to split the ground or saving people from fatal attacks. She is exceptionally sensitive to the flow of Tao in others, allowing her to sense when Gabimaru is missing a part of his spirit or when an enemy possesses a dangerous amount of power. Her Tao is also unique in that it can affect the physical maturity of her own body. In her Kishikai transformation, she gains the ability to fly and generate powerful waves of wind. Her knowledge of Tao is her greatest asset, as she serves as the instructor who helps the human characters unlock their latent potential by teaching them to sense the Tao within themselves and in nature.