Kari Tsukumo, known as Akari Tsukumo in the original Japanese version, is the twenty-year-old older sister of the main protagonist Yuma Tsukumo in Yu-Gi-Oh! ZEXAL II and the original series. As a working journalist, she takes on the primary responsibility of providing for her younger brother and their grandmother, Haru Tsukumo, following the absence of their parents. Her daily life is driven by a relentless pursuit of the next major news story, a dedication that often sees her working from her home computer or chasing leads across Heartland City. Despite her professional drive, her most defining characteristic is her fierce, if often aggressive, protectiveness over Yuma.

Her personality is a blend of sharp professionalism and volatile emotion. Kari is highly competent, possessing a black belt in karate and impressive skills in computer hacking, which she has used to directly confront digital threats. She is also a skilled driver, capable of maneuvering her car, a memento from her father, and a motorcycle left behind by a past love interest, with considerable daring. However, she is also short-tempered, impulsive, and can be domineering, frequently shouting at or physically intimidating her brother. This aggressive exterior masks a deep-seated care and sense of duty. In a promise made to her parents, she swore to look after Yuma, a vow that shapes her actions even when her methods are overbearing. A trace of her more vulnerable past is seen in her lingering feelings for a gambler named Charlie McCay, whose sudden departure after a kiss left her with unresolved emotions.

Throughout the story, Kari's primary role is that of a guardian and a foil to Yuma's dueling adventures. Initially, she is adamantly opposed to Yuma dueling, forbidding him from participating for reasons tied to a promise made to their father who feared the dangers Yuma would face. She spends much of the early series trying to catch him in the act, only to eventually relent after witnessing his duels firsthand and gaining confidence in his ability to protect himself, a philosophy tied to his catchphrase of "kattobingu". Her profession frequently intertwines with the plot, as she sends Yuma to investigate dangerous situations for her scoops, inadvertently placing him at the center of conflicts involving the Numbers and the World Duel Carnival. Beyond her relationship with Yuma, she has key connections to other characters. She is close friends with Bronk Stone's older sister, Brianna, and shares a complicated history with the gambler Charlie McCay, whose reappearance forces her to confront her past.

Kari's development is subtle but noticeable. She evolves from a strict, prohibiting guardian into a more supportive, if still exasperated, family member who allows Yuma to follow his own path. Her confidence in his abilities grows to the point where she actively assists him, such as using her driving skills to stop a runaway train during his duel with Charlie. In Yu-Gi-Oh! ZEXAL II, her role becomes more peripheral, though she remains a consistent presence, often shown worrying about Yuma at home or scolding him for reckless behavior that lands him in the hospital. Her notable abilities extend beyond physical combat and hacking to include remarkable strategic thinking, as she was able to deduce the weakness of Charlie's Number card, Lucky Straight, providing Yuma with the key to victory. She is a capable yet often understated force, representing the grounded, everyday world from which Yuma constantly ventures into the extraordinary.