Yasuko Tanaka possesses brown hair, blue eyes, and an overweight build. She discovered the treasure of the pirate Throlla, an event during which she was cast overboard from her ship. This ordeal resulted in her acquiring the mythical weapon, Gallon's Hammer, which she now wields.

Her narrative role involves the relentless romantic pursuit of Issei Ariga, a former member of the Shoshidai organization. Her advances caused Issei significant discomfort and contributed to his departure from the Shoshidai. Their interactions culminated in a sexual encounter that Issei later regretted, despite acknowledging Yasuko's physical attractiveness.

Yasuko's possession of Gallon's Hammer places her within the broader conflict surrounding cursed weapons. While her actions and pursuit of Issei intersect with ongoing events, her direct involvement in major battles or the central plot remains limited. She is identified as a treasure hunter.