TV-Series
Description
The Obsidian Goddess, originally named Kokuyō no Megami, exists mysteriously within Musashi. Pursued by the Obsidian Eight for her significance and powers, she originated as one being with the first Black Demon God. She betrayed and separated from him to find an ally capable of stopping him.

She encountered the near-death bushi captain Shiro Inukai after a demon invasion. Saving him, she injected a black heart into his body and provided the first Kitetsu Sword, marking him as history's first bushi wielder. The black heart corrupted Shiro, stripping his emotions and driving him to violence. Viewing this corruption as part of her own sins, the Obsidian Goddess abandoned Shiro's band. She wandered alone for a century, fighting Oni demons, until finding a new host in Seigen Toda.

During Musashi's Kitetsu Blade trial in the Daito Mine arc, she interfered, causing his failure. Later, when Musashi confronted Shiro and was thrown into a pit, she trapped him in a magma-filled void. She urged him to abandon his friends and remain with her forever, invoking his traumatic past, including the loss of his parents, to break his spirit and evade the Obsidian Eight. Musashi's allies intervened, pulling him from the magma and thwarting her plan.

Facing mortal danger from Shiro and Nanao Inusaka alongside his allies, the Obsidian Goddess stopped time. She offered Musashi her power to save himself alone. He refused, emphasizing reliance on comrades. Recognizing his ability to unite others as valuable against the Kishin, she temporarily seized control of Musashi's body. Using his form, she drew energy from all nearby Kitetsu Blades, seized Shiro's blade, and repelled attacks, including Nanao's, by manipulating blade energy magnetism. This power stems from her nature as the ruler of Kitetsu Swords, allowing her to attract or repel blade energy and cause disorientation.

After this display, she explained her fragile existence and the need to return to dormancy within Musashi, causing him to lose her powers. She questioned if his allies would continue supporting him once aware of her presence, though they affirmed loyalty. She rejected Shiro's plea to join him. Borrowing energy from the bushi, she unleashed a devastating attack obliterating multiple hills before returning to sleep within Musashi. She emphasized his role as her vessel and hinted at unfinished business concerning Jisai.

The Obsidian Goddess possesses critical abilities. As ruler of Kitetsu Swords, she utilizes all blade energy colors. Sharing her blood with Musashi unlocks his access to these colors, such as yellow soul. She controls blade energy magnetism, warps or repels attacks, and draws power from any nearby Kitetsu Blade. She can stop time and light. Her presence enables spatial transference and mass manipulation. Her powers are tied to black stones granting control over blade energy.

She has long fair-colored hair, sometimes accompanied by a halo, and freely shifts between an adult woman's form and a teenager's. Her motivations include evading the Obsidian Eight, who seek to use her as a "compass" to locate divine treasures and ensure the Kishin's survival. Her relationship with hosts like Musashi balances protection against corruption and exploitation of her powers.