- Birth Name: Matsubara Natsumi (松原夏海)
- Nickname: Nattsumii (なっつみぃ)
- Date of Birth: June 19, 1990
- Place of Birth: Fukuoka, Japan
- Blood Type: B
- Height: 160cm
- Bands / Groups:
- [2013.05.08] Kasai Tomomi - Mine (Type-B) (#3 Enjoy your life! (with Akimoto Sayaka, Umeda Ayaka, Oshima Yuko, Ohori Megumi, Kobayashi Kana, Noro Kayo, Matsubara Natsumi, Miyazawa Sae))
- AKB48 Song Participation
- Aitakatta (会いたかった)
- Sakura no Hanabiratachi 2008 (桜の花びらたち2008)
- "Iiwake Maybe" single
- Tobenai Agehachou (飛べないアゲハチョウ) (Under Girls)
- "RIVER" single
- Hikoukigumo (ひこうき雲) (Theater Girls)
- "Ponytail to Chouchou" single
- Boku no YELL (僕のYELL) (Theater Girls)
- "Heavy Rotation" single
- Namida no Seesaw Game (涙のシーソーゲーム) (Under Girls)
- "Beginner" single
- Nakeru Basho (泣ける場所) (DIVA)
- "Chance no Junban" single
- Kurumi to Dialogue (胡桃とダイアローグ) (Team A)
- "Sakura no Ki ni Narou" single
- Area K (エリアK) (DIVA)
- "Everyday, Katyusha" single
- Hito no Chikara (人の力) (Under Girls)
- "Kaze wa Fuiteiru" single
- Vamos (Under Girls Baragumi)
- "Ue kara Mariko" single
- Rinjin wa Kizutsukanai (隣人は傷つかない) (Team A)
- "GIVE ME FIVE!" single
- Jung ya Freud no Baai (ユングやフロイトの場合) (Special Girls C)
- "Manatsu no Sounds good!" single
- Mittsu no Namida (3つの涙) (Special Girls)
- "Gingham Check" single
- Ano Hi no Fuurin (あの日の風鈴) (Waiting Girls)
- "UZA" single
- Scrap & Build (スクラップ&ビルド) (Team K)
- Eien Pressure (永遠プレッシャー)
- "So long!" single
- Yuuhi Marie (夕陽マリー) (Oshima Team K)
- "Sayonara Crawl" single
- How come? (Team K)
- "Labrador Retriever" single
- Kyou Made no Melody (今日までのメロディー)
- Stage Units
- Team K 1st Stage "PARTY ga Hajimaru yo"
- Classmate (クラスメイト)
- Kurukurupaa (くるくるぱー)
- 16nin Shimai no Uta (16人姉妹の歌)
- Saboten to Gold Rush (サボテンとゴールドラッシュ)
- [2010.12.xx] Artist File BIG ONE GIRLS No.4 (Feature)
- Originally a member of Team K, she was transferred to Team A during the AKB48 team shuffle in August 2009. She was transferred back to Team K during the team shuffle in August 2012.
- Catchphrase: "min min min Nattsumin!" (みんみんみん なっつみん!)
- Her oshimen is Iwasa Misaki.
- Favorite food: Hot pot
- Favorite drink: Vegetable juice
- Favorite artist: Fergie, Bon Jovi
- Favourite drama: Umizaru
- Favourite manga: Tenshi Nanka Janai
- Favorite magazine: Jelly
- Favorite season: Spring, Summer
- Favorite brand: Spiral Girl
- Favourite colour: Marine blue.
- Favourite smell: Soap.
- Favourite word: 「一期一会」 ("A once-in-a-lifetime encounter.")
- Favourite school subject: Maths.
- Favourite sport: Volleyball.
- Favorite AKB single: Baby! Baby! Baby!
- Favorite AKB stage song: Tadaima Renaichuu
- Favorite AKB outfit: The K5th Encore outfits
- Charm point: Her shoulders, the fingernail of her ring finger
- Special skills: Conversation skills, calming small children
- Habit: Chewing things.
- Likes detective novels and has read all of the Sherlock Holmes series.
- The first CD she ever bought was a Britney Spears album.
- Her favorite Sailor Moon character is Sailor Venus.
- Plays Final Fantasy games on rainy days.
- Used to swallow her marbles as a child.
- Is the very middle of five siblings - an older brother, an older sister, her, a younger sister and a younger brother. Her older sister is three years older than her, and her younger brother Yuito is fifteen years younger.
- Hobbies: Making sweets, nail art, personality tests, watching Movies