Mu is the Gold Saint of Aries, a guardian of the first temple in the Sanctuary and one of the most powerful warriors serving the goddess Athena. He is known throughout the world of the Saints as the Cloth Blacksmith, the only person capable of repairing sacred cloths that have been damaged beyond natural regeneration. Mu was born in Tibet and trained under his mentor Shion, the former Aries Saint who became the Grand Pope. When he suspected that Shion had been secretly assassinated, Mu distanced himself from the Sanctuary and relocated to the mystical land of Jamir, a place accessible only to those with high psychic or Cosmo power. There he lived in seclusion with his young apprentice Kiki, refusing to involve himself in Sanctuary politics for many years.

Mu possesses a calm, soft-spoken, and scholarly demeanor. He is logical and even-tempered, never letting emotions override his reasoning. This rational nature can sometimes appear cold or detached, yet he is not without compassion. He tests the resolve of those who seek his aid, as seen when he required Dragon Shiryu to offer his blood for a cloth repair, but he immediately intervened to save Shiryu when the blood was no longer necessary. Mu is cautious and does not act rashly; although he long suspected the Pope was evil, he chose not to oppose him directly until the truth could be proven. His motivations center on protecting Athena and preserving the harmony of the Sanctuary, but he prefers to work behind the scenes rather than engage in open conflict unless absolutely necessary.

In the story of Legend of Sanctuary, Mu first appears when the Bronze Saints arrive at the Aries Palace. He confronts Pegasus Seiya with a defensive technique, the Crystal Wall, but only to test their strength. After a brief exchange, he reveals that he is actually an ally and allows the Bronze Saints to continue through his temple. He remains a key supporter of Athena’s cause, watching over Saori Kido and providing guidance to the young warriors. Alongside Taurus Aldebaran, he becomes one of the few Gold Saints who openly side with the goddess during the conflict against the false Pope. His relationship with Aldebaran is one of mutual respect and friendship, and he holds great reverence for the ancient Libra Saint Dohko, the master of Dragon Shiryu.

Mu’s abilities are exceptional even among the Gold Saints. He wields the most powerful raw psychic powers of any living Gold Saint, manifesting through telekinesis, telepathy, and teleportation. His signature techniques include the defensive Crystal Wall, which forms an impenetrable barrier; the Crystal Net, which ensnares opponents; and the devastating Stardust Revolution, an offensive cosmic blast. He also commands the power of light-speed movement, a hallmark of those who have mastered the Seventh Sense. His skill in repairing cloths involves the use of mystical materials such as Orichalcum, Gammanium, and Stardust Sand, requiring a portion of the Saint’s blood to complete the restoration. Over the course of the film, Mu evolves from a secluded observer into an active protector, demonstrating that his loyalty to justice outweighs his natural caution.