Wendy Sato, 21, balances accounting and clerical duties at Pinochle's Old Maid branch with her true role: recovering scattered X-Playing Cards for the secret organization High Card in the Kingdom of Fourland. Her serious, unfriendly nature often clashes with more relaxed colleagues like Finn and Chris, causing friction. Despite this generally cold demeanor, she possesses a marked enthusiasm for food and drink, exceeding other High Card members; alcohol consumption specifically shifts her into a noticeably sunnier, cheerful mood.

Her High Card position stems from connections to her father, a master swordsman from the Far East, influencing both her team role and weapon choice when using her assigned card. She wields the Ace of Spades, "Love and Peace" (♠A 《Love and Peace》), which manifests a powerful sword. She can partially deploy this sword for enhanced combat ability. However, fully drawing the weapon triggers a drastic transformation into the homicidal alternate personality "Love-P" (LAP), driving her to kill everyone nearby. This state persists until the sword is physically removed from her grasp.

Operating alongside teammates including Finn Oldman, Chris Redgrave, and Leo Constantine Pinochle, her commitment to High Card's objectives remains firm, even as her serious disposition frequently puts her at odds with their methods.