Mu Dan is one of the Lord Tensen, the immortal rulers of the mysterious island Shinsenkyo, also known as Kotaku, and serves as a major antagonist in the story. His name means peony in Chinese and Japanese, and he is also referred to as Enthroned Amoghavajra. Mu Dan is an ancient being who has lived for centuries, accumulating vast knowledge and power through his mastery of Tao, the fundamental energy of the world. He possesses Earth-attribute Tao and is particularly skilled in its manipulation, allowing him to launch invisible Tao projectiles, enhance his physical strikes to cause internal damage, conceal his presence, and even fly by controlling Tao in the air. His abilities also extend to sensing the intentions of others and predicting attacks.

Mu Dan typically maintains a male form, though like all Tensen he can shift between a Yang male body with a well-toned, muscular build and a Yin female body with a slender, feminine appearance, reflecting his complete control over Yin and Yang energies. Physically, he has short red hair that resembles flower petals and golden eyes.

In terms of personality, Mu Dan presents a calm and welcoming demeanor, often wearing a serene smile, but this masks a deeply sadistic and cruel nature. He derives great pleasure from inflicting pain and suffering on humans, and he treats those he captures as toys or servants. He is intensely curious about human minds and behavior, and has studied the mainland for two centuries to understand how people think and live outside of Kotaku. Among the Tensen, he is known as the most battle-hungry and aggressive, actively seeking out strong opponents to fight. He enjoys sharing knowledge about Tao with those he finds interesting, much like his fellow Tensen Mei does with Gabimaru.

Mu Dan’s role in the story is that of a powerful and dangerous antagonist who must be confronted by the expedition team. He uses his Tao to control the Soshi (island creatures) and even humans, turning them into living puppets to fight on his behalf. This makes him a formidable opponent in group battles, requiring coordinated efforts from multiple characters such as Sagiri, Yuzuriha, and Senta to finally defeat him. He views humans primarily as sources of Tan, a vital substance for the Tensen’s continued existence, and he treats them with cold indifference or outright cruelty.

His most devastating ability is the Kishikai transformation, a monstrous form that amplifies his power. In this state, he can summon deadly vines tipped with flower-shaped stingers that induce Arborification—a process that slowly turns living tissue into plant matter—upon contact. He can also fire devastating Tao lasers from this form. Mu Dan possesses remarkable regenerative capabilities, characteristic of the Tensen, allowing him to recover from injuries as severe as decapitation. He can even control which parts of his body regenerate, and he can shift between Yin and Yang chi to replenish his Tao and alter his physical form accordingly.

Mu Dan’s key relationships are primarily with the other Lord Tensen, as they are all ancient beings sharing the rule of Kotaku. He has a notably curious and analytical approach to human characters, especially those who prove to be strong or unusual, such as the shinobi Yuzuriha. However, he shows little genuine attachment or loyalty beyond the Tensen collective. Throughout the series, his development is minimal in terms of personal change; he remains consistent in his sadism and obsession with understanding humans, ultimately meeting his end at the hands of the combined efforts of the human protagonists who exploit his weaknesses in Tao balance.

Overall, Mu Dan stands as a chilling embodiment of immortal power twisted by centuries of detachment from humanity, using his intellect and Tao mastery to toy with and terrorize those who enter his domain.