Jeri Kato, known in the original Japanese version as Juri Kato, is a central character in Digimon Tamers. She is a classmate of the protagonist Takato Matsuki and initially appears as a cheerful and slightly eccentric girl, often seen with a homemade dog-shaped sock puppet on her hand, through which she sometimes speaks. She comes from a family that runs a small restaurant, where she occasionally helps with serving. Her home life is more complicated than it first appears; her birth mother died from an illness when Jeri was very young, and her father later remarried. Jeri struggled to accept her kind stepmother, feeling that accepting her would mean erasing the memory of her real mother. She also has a younger half-brother, Masahiko, whom she often entertains with her puppet.

At the beginning of the series, Jeri is not a Digimon Tamer. However, unlike some of their other friends who reacted with fear, she was quick to befriend Takato's partner, Guilmon, showing her open-minded and caring nature. It is also revealed that she has a collection of rare Digimon cards, which sparks a friendship with the more experienced and initially aloof Rika Nonaka. Jeri's cheerful personality is presented as a genuine desire to encourage her friends, but it also serves as a facade to hide her deep-seated sadness and feelings of unworthiness, stemming from her mother's death and her belief that she was fated to be alone.

Jeri's role in the story becomes crucial when she finally becomes a Tamer, receiving a yellow D-Ark Digivice and forming a partnership with the noble lion Digimon, Leomon. While initially star-struck by him, she proves to be a capable and creative Tamer. A key example of her developing skill is when she uses a rare Lady Devimon card to grant Leomon the power to defeat the powerful Orochimon who had kidnapped her. Her journey into the Digital World alongside the other Tamers solidifies her bond with Leomon, who recognizes her inner strength and tells her she has "a lion's heart".

The tragic turning point for Jeri comes when the destructive Digimon Beelzemon kills Leomon and absorbs his data. This event shatters her emotionally, plunging her into a deep depression. Her cheerful mask falls away as she becomes withdrawn and consumed by grief, believing the death was her fault and that her destiny is to suffer loss. This profound despair makes her a perfect target for the D-Reaper, a sentient program that threatens both the Digital and real worlds. The D-Reaper captures Jeri and imprisons her within a kernel of its being, using her negative emotions to study humanity and power itself.

While the real Jeri is trapped, the D-Reaper creates an agent in her form, the Jeri-Type Agent, to infiltrate the Tamers. This doppelgänger initially fools her friends. Inside the D-Reaper, Jeri remains catatonic, lost in her grief, until her other small friend, Calumon, and even a guilt-ridden Beelzemon attempt to rescue her. It is through this ordeal that Jeri begins to fight back, understanding that she must reject the fatalistic idea of "destiny" that has haunted her since her mother's death and that Leomon's last words to her were a call to be strong. Her unwavering friendship with Takato, who risks everything to save her, is a central part of her recovery.

Throughout the series, Jeri's key relationships are central to her development. Takato has a clear crush on her, and by the end, it becomes evident she reciprocates his deep care for her. Her friendship with Rika evolves from a mentorship to a strong mutual respect. Her bond with her partner Leomon is one of mutual empowerment, and his death is the catalyst for her deepest trial. Finally, her ability to forgive Beelzemon for murdering Leomon demonstrates her immense capacity for compassion and her ultimate emotional growth.

Jeri's notable ability as a Tamer is not in physical combat but in her strategic use of the Digi-Modify cards to enhance her partner's abilities in creative ways. Her most significant feat is successfully using the powerful Lady Devimon card, a level of skill that surprises even her more battle-hardened friends. Ultimately, her greatest strength is her emotional resilience. Despite being consumed by despair and used as a tool by an eldritch entity, she finds the inner strength to reject her pain, forgive those who wronged her, and reclaim her destiny. By the end of Digimon Tamers, Jeri emerges from her ordeal able to face the future with genuine hope, having truly earned the "lion's heart" Leomon always believed she had.