|Birthday||January 25, 2000|
|Relations||Komari Koshigaya (older sister)|
Suguru Koshigaya (older brother)
Yukiko Koshigaya (mother)
Natsumi Koshigaya (越谷 夏海 Koshigaya Natsumi?) is one of the main characters of Non Non Biyori series. She is the youngest of the Koshigaya siblings and the one who makes most of the ideas to have fun with everyone.
She has orange-red hair and blue-grey eyes. Her hair usually looks messy in a half up half down do. She wears clothes that are quite boyish and easy to run in.
She is fun-loving and irresponsible. She makes most of the fun ideas for everyone. She tries to get out of trouble or responsibility by blaming it on others (even objects) and hiding proof of bad things she does. She is very energetic and can't sit still for long, often fidgeting in her chair. She often teases her older sister, Komari. She's often scolded by her mom due to her grades or messes. Out of the three older girls, she seems to be the one who gets along the best with Renge, often taking her questions seriously and sometimes calling the other characters by Renge's nicknames for them. She also calls Renge "Renchon."
- Her name means "Summer Sea" in the kanji given.
- She admitted that she has a girly side.
- She is 155 cm tall.
- She once said, when she was really young, that she would marry her brother.
- Renge's nickname for her is "Nattsun".
- Her nickname for Renge is "Ren-chon".
- It is shown that she is very knowledgeable in extracurricular things despite being bad at academics.