She and her brother live with their grandmother Haru. Kari doesn't let Yuma Duel, according to the manga, Astral thinks it has something to do with the Emperor's Key. However, Haru seems to allow Yuma to Duel without Kari finding out. In Episode 16, she discovered that Yuma had been Dueling despite her opposition, but apparently does not mind and now permits him to Duel.
Kari can be a tad self-centered at times, occasionally sending others out to find her scoops to make reports on, even if it is dangerous or hazardous. She can also be a tad aggressive, showing to be willing to physically attack Yuma when she caught him dueling (though it is possible she was just trying to intimidate him).
Despite this, Kari genuinely cares for her little brother, and seems to be rather protective of him. She made a promise to her parents that she would do what she can to take care of Yuma, being told that he would rely on her for a long time. As a teenager, she seemed jealous that Yuma got more attention from their parents but has seemingly gotten over any animosity she may have had then. Also, Kari's car was a memento from her father, and she drives it with great care.
In the past, Kari and Yuma were very close and didn't like the fact that their parents went on so many trips. When her father injured himself during a snowstorm accident, she noticed the pendant in his hand as he was being taken to hospital.
In the past, Kari was also very jealous of the attention that Yuma received from their parents as he is the youngest. Her parents notice this and tell her that even though she thinks it, it isn't true and that they pay more attention to Yuma because he is frail, and that they will rely on Kari to look after Yuma while they go on trips.
It is also shown that while Kari was at high school, she developed a relationship with Charlie McCay, a gambler who was known for being a daredevil. One night, he kissed Kari before driving away on a motorbike. It is assumed that he never returned after promising her he would. She kept his motorbike as a memento next to her garage and drives it sometimes when she finds out about a hot scoop which requires her to be swift. It should also be noted that she also uses her father's car while he lived with them for driving around.
Kari is first seen during the day when Reginald Kastle snaps her brother's pendant, which their father gave him. Yuma moans at her for not waking him up, but she pushes Yuma's comment back by saying that because he's in middle school, he should wake himself up, causing Yuma to pull a face. She then continues with her work and takes a drink from a cup, ignoring Yuma's annoyance.
The day after Yuma beat Reginald, a freak virus caused Heartland City to malfunction not only causing distress for the various civilians, but also caused Kari's computers to shut down, losing a precious scoop which she had been working on for days causing her to scream. Yuma, hearing this, ran to see what was wrong, but in turn Kari blamed Yuma for the accident causing him and his friends to run in fear. She then picked Yuma and Tori up from Heartland Middleschool and tells them that she managed to find the location of the person who uploaded the virus, that being in the schools library thus forcing Yuma and Kari to scope the location out for anyone suspicious.
She is later informed of a virus which was set to attack the city via her computer. Straight away she began to hack through the cities systems in order to locate the virus and stop it for a great scoop. She reveals here that she is a black-belt in karate and begins to attack the virus via her computer counterpart. Even though Kari manages to defeat the Bugman guarding the virus, it was too late. Although this is said, the virus turned out to merely cause a giant Crashbug to appear above the Crashbug Stadium and throw bombs which produced fireworks which bought happiness to the children within Heartland City. After Yuma receives the fan-mail from Flip containing the Baby Tiragon card, Kari shows her annoyance by warning Yuma that he better not be Dueling. She then looks at Haru Tsukumo in annoyance which causes her grandma to pull a scared face and look away, pretending she didn't hear the conversation and carries on drinking her tea.
Always looking for a scoop, Kari notices on the news that there is a criminal keeping many people hostage at the Heartland Shopping Mall, she instantly rings Yuma on his Duel Gazer and asks him where he is, although he tried to deny being at the mall, Kari knew he was there thus screamed at him to get her some information on the occurrence. Before Yuma could get close to the scene, Kite Tenjo and Orbital 7 caused the time to freeze allowing them to capture the criminals Numbers without anyone interrupting. Yuma and Astral realized that they could move around in this frozen time, but several blockages cause Yuma to get there just before Kite turns the time back to normal, thus the police attack Yuma, messing up Kari's scoop as it was reported all over the news, thus would be old.
After Yuma visited the Duel Sanctuary and began his Duel with Kaze to defend the lodge, Kari and her grandma came to see where Yuma was and walked in just as the Duel had begun. Seeing Yuma Duel annoyed Kari and she was about to punish him for it, but was stopped by Roku who told her that Yuma could only grow through Dueling and that she must witness Yuma Duel. Ever since Yuma defeated Kaze, Kari has confidence that Yuma will be safe and believes in his "Kattobingu" spirit.
During the parents day at Yuma's middleschool, Kari attends a reporter party unknowning of the events occuring at Yuma's school as he didn't tell her or Haru about it. At the party, Kari meets up with Bronk's sister: Brianna Stone who is also a friend of Kari's, she questions Kari why she didn't go to the event which causes her to run out and go to the school as she promised her parents that she would protect and look after Yuma. She alerted Haru and both turned up to the event and scolded Yuma for not telling them and to later support him in his '20 stack challenge'.
World Duel Carnival
One night while Kari was preparing her work, a robbery in the Heartland Museum was reported on her computer. Suddenly her Duel Gazer lit up and it turned out that her old romance, Charlie McCay was the one behind the robbery and wanted Kari to help him. Before Kari could decline, Charlie hung up. Annoyed at Charlie and how he left Kari in the past, she sent Yuma to do her work for her. After Yuma located Charlie, he challenged him to a Duel and the latter was surrounded by the Heartland police, who tried to subdue him, but by using the powers of "Number 7: Lucky Straight", he was able to escape and cause massive destruction, even managing to steal a large amount of cards from the people in the vicinity including Yuma's "Number 11: Big Eye". Kari then met up with Yuma and Tori, who told her what happened. Determined to find him, all three set off.
After Yuma and Tori trapped Charlie on a subway train, Kari followed them and watched the Duel on her motorbike. After Yuma defeated Charlie, Kari stopped the train by sliding her motorbike into the rails, forcing it to stop. She began to scold Charlie for what he did and even wanted to know about a girl named May he was talking about, but she learned of his true intentions as he wanted to take "Lucky Straight" so that he could give luck to his niece, May, who was undergoing an important operation. Later that night, Kari and Charlie walked through the streets of Heartland City and Charlie kissed Kari, but received a slap across the face as she didn't want a repeat of last time (cut from the dub). He then wandered off into the night, leaving Kari dazed.
After Kari was appointed with the task of finding Cameron, she was angered upon learning that he hurt people with his predictions. When Yuma Dueled him, she was seen trying to keep Tori calm (who was on the plane Cameron predicted was going to crash), and also even trying to get the people in charge of the blimp to stop it. She was surprised when Kite came in her view, and recognized him.
Later when she learned that Yuma was going to leave to go find his father Kazuma Tsukumo, she was not happy with his decision. Like the others though, she was happy when he decided not to leave.
After Yuma's victory over Vetrix, she drove to Heartland to check what was going on, but was surprised that Yuma and Tori were still inside, causing her to worry. After a brief conversation with Tori over her phone, she began to worry again.
Yu-Gi-Oh! ZEXAL II
Following Yuma's Duel with Mizar, Kari was seen at the hospital yelling at her brother for endangering his and Shark's lives. Rio appeared and told her to quiet down as Shark was resting. Kari apologized, told Yuma that he was lucky that his and Shark's injuries weren't serious, and left. When Lillybot returned home from buying groceries, Kari thanked Lilly and made a rude comment toward Yuma. One night at dinner, Yuma was eating his dinner at a fast pace, which caused Haru to asks why he's acting differently. Yuma replies by thanking her for everything and asks Kari if she's busy for work. This startled her, causing her to ask him what got into him. Yuma then got up and starts massaging her shoulders, much to her chagrin. After dinner was over, while Haru and Kari were washing the dishes, the latter asked her grandmother why Yuma was acting differently and what he was planning. Haru replied that Yuma was like Kazuma because he acted that way before leaving on a big adventure. This caused Kari to get upset and leave to stop Yuma, but Haru stopped her. She told her that all they can do is watch over Yuma. The next day, when Yuma tried to leave his home, Haru calls out to him. Surprised, Yuma turned around and found his family waiting for him at the door. Lillybot tossed Yuma some Duel lunch and Kari told Yuma to come back for dinner before voicing her support for her brother.
When Yuma returned home, Kari was upset at Yuma for getting Tori involved with the search of the "Mythrian Numbers".. Later, she was frustrated that she could not connect to any online systems. Kari was also annoyed by Lillybot cleaning up the place, up to the point that she kicked her across the room. The Litterbot subsequently reactivated, much to Kari's surprise and Lillybot fixed the screens to watch Kite's Duel against Mizar. A confused Kari asked what was going on, and Lillybot explained that Orbital was fighting for the sake of everyone on Earth. Kari and Lillybot then watched the Duel.
Before the final Duel between Yuma and Astral, Kari complained about the mess that Yuma's friends made. She became embarrassed when Haru suggested that she Duel to find a husband. Kari was last seen getting into another argument with Yuma.