Yuamu Ohdo is the younger twin sister of Yuhi Ohdo and serves as president and CEO of the Ultraterrestrial Tracker Squad (UTS), an organization resolving alien-related issues. Both twins are ancestors of Yuga Ohdo. Initially, Yuamu possesses pale skin, purple eyes, and waist-length brown hair featuring red highlights in the bangs and emerald green beyond the shoulders. She typically sports an orange jumpsuit tied at the waist, a teal blouse, a white cropped jacket, white gloves, pink-and-white striped socks, and distinctive magenta-framed glasses offering thermal and telescopic functions. Later, her school uniform comprises a sailor-style blouse, blue pleated skirt, and brown Mary Jane shoes. Casual outfits incorporate elements like purple shorts, mismatched black stockings, and red skirts with striped socks.

Yuamu embodies a highly intelligent, pragmatic, and calm personality, strategically leading UTS with sharp business acumen. She adeptly identifies opportunities for organizational gain, such as recruiting Yudias Velgear after recognizing his interest in Rush Duels. She maintains a dominant yet trusting dynamic with Yuhi, directing him during UTS operations while supporting his dueling capabilities. Following exposure to Yuga Ohdo's memories during a dark matter storm concluding the second season, she resolves to ensure his future by becoming "Otes." This quest takes her to the Dark Matter Space, where she founds the Dark Matter Empire under the alias "Dark Meister," emerging as the primary antagonist for the third season. As Dark Meister, her appearance transforms: her skin turns lilac, her hair elongates into purple-black spirals reaching her feet, and she dons elaborate purple-and-gold robes, a butterfly mask, an amethyst necklace, and a floating crown. After her identity reveal, she wears a black dress with burgundy lining, heart motifs, thigh-high leggings, and red boots.

In dueling, Yuamu utilizes a Light-attribute "High Tech" Dragon deck centered on technological computer-themed monsters and aggressive tactics. After establishing the Dark Matter Empire, she switches to a Darkness Galaxy deck featuring dark matter-corrupted dragon monsters. This deck leverages effects triggered by face-down cards and introduces Contact Fusion, enabling Fusion Summons without Spell Cards. Her recorded duels include victories against Chupataro Kaburagi, Manya Atachi, The☆Yeti Yukio, Asaka Mutsuba, and Zuwijo Zwil Velgear, alongside losses to Phaser Ryugu and Yudias Velgear during pivotal confrontations.

Following her entry into the Dark Matter Space, Yuamu gains powers beyond dueling to manipulate dark matter, crafting structures like the Dark Matter Castle and imbuing objects with dark energy. Her plan to erase her memories using "Monster Reborn" and become Otes ultimately fails when Yuhi assumes that role instead. After Yudias defeats Yuhi-as-Otes, Yuamu loses her dark powers upon being transported to the Sengoku era via a time machine. She later aids in Otes's final defeat before returning to her original timeline with Yuhi.