|Portrayed By||Kaori Mizuhashi|
Natsumi is the daughter of Haruko Kimiyoshi and Touji Kimiyoshi. The family moved from Okinomiya to the city with Natsumi's grandmother, Aki Kimiyoshi who was a native of Hinamizawa and devout believer of its local deity, Oyashiro. She becomes friends with classmates Chisato Saeki and Tamako Makimura and later develops a crush on Akira Toudou, who likes her in return.
Natsumi appears as a young girl with olive-green hair and orange eyes. She typically wears a light pink school uniform with orange highlights. When not at school, Natsumi wears a striped pink top and a plaid skirt. In Higurashi no Naku Koro ni Kizuna, Natsumi's hair is noticeably greener than in Higurashi no Naku Koro ni Matsuri.
After the Great Hinamizawa Disaster, many former Hinamizawa residents begin to act strangely. Kuraudo Ooishi and Mamoru Akasaka come to Natsumi's house to talk to her grandmother who they heard was from Hinamizawa. At the time, however, she isn't home. She is taken to a restaurant and is questioned by them. Akira comes by them and says that people wearing school uniforms can't go inside restaurants. Outside, Natsumi thanks him, and he volunteers to take her home. Upon arriving at her house, there are talismans all over it. Akira walks away, and Natsumi runs into her house. Her grandmother is performing rituals to cleanse her family (such as drowning puppies), and she calls her mother. The next day, she tells Akira that her family is related to the Hinamizawa incidents, and he believes her.
One day, after arriving home from school, she sees her grandmother being attacked by Haruko. In the end, her grandmother dies. Haruko suggests cutting her into small pieces, so they can hide her better. At school, the next day, her friends notice her behaving strangely and note that there's a rumor circulating about Natsumi being from Hinamizawa.
On her way home from school, she sees a news cast about a body of an elderly woman being found. Upon arriving home, she sees her mother beating her father for hiding the body in an easy-to-find spot. After she leaves the room, Natsumi's father suggests calling the police. However, Haruko comes back into the room and stabs her husband's neck. Then, she decides to kill Natsumi.
Akira calls Natsumi's house from a payphone and hears someone screaming for help. Upon arriving at Natsumi's house, Haruko seemingly strikes him with a vase. Natsumi tries to wrestle the knife out of Haruko's hands and Haruko accidentally slices her own neck open in the struggle. Natsumi is rescued by Akasaka and the police and Natsumi apologizes to Akira for lying to him.
Later, when Akira confronts her, it is revealed that Natsumi's testimony was fabricated, and she was actually the one who killed her family. In a fit of psychosis, she ends up stabbing him in her confusion. However, shortly afterward, she realizes that Akira is the only important thing she has left.
In the epilogue, it is revealed that Natsumi was being cared for by other members of the Kimiyoshi family for a few years. However, they believed she was cursed by Oyashiro-sama and had her locked in a room filled with talismans, bound and blindfolded. Akira saves her and they get married and move to a small, rural town. She was too unstable to live in a house, so she lives in a local clinic where Akira visits often.