- Name: Hirajima Natsumi (平嶋夏海)
- Nickname: Nacchan (なっちゃん)
- Birthdate: May 28, 1992
- Birthplace: Tokyo, Japan
- Blood Type: O
- Height: 154cm
- Bust: 80cm
- Waist: 56cm
- Hips: 83cm
- Click here for Watarirouka Hashiritai releases
AKB48 Song Participation
- Sakura no Hanabiratachi (桜の花びらたち)
- Skirt, Hirari (スカート、ひらり)
- Sakura no Hanabiratachi 2008 (桜の花びらたち2008)
- "Oogoe Diamond" single
- Oogoe Diamond (teamA ver.) (大声ダイヤモンド) (Team A)
- "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
- Boku Dake no value (僕だけのvalue) (Under Girls)
- "Chance no Junban" single
- Love Jump (ラブ・ジャンプ) (Team B)
- "Sakura no Ki ni Narou" single
- Area K (エリアK) (DIVA)
- "Everyday, Katyusha" single
- Hito no Chikara (人の力) (Under Girls)
- "Flying Get" single
- Dakishimecha Ikenai (抱きしめちゃいけない) (Under Girls)
- "Kaze wa Fuiteiru" single
- Vamos (Under Girls Baragumi)
- "Ue kara Mariko" single
- Yobisute Fantasy (呼び捨てファンタジー) (Team B)
- "GIVE ME FIVE!" single
- Jung ya Freud no Baai (ユングやフロイトの場合) (Special Girls C)
- "Koisuru Fortune Cookie" single
- Suitei Marmalade (推定マーマレード) (Future Girls)
- Hoshi no Ondo (星の温度) (2nd Unit)
- Nage Kiss de Uchiotose! (投げキッスで撃ち落せ!)
- Pajama Drive (パジャマドライブ)
- Kuchiutsushi no Chocolate (口移しのチョコレート)
-  Ashita no Watashi no Tsukurikata (あしたの私のつくり方)
-  xGame 2 (×ゲーム2)
-  Hadaka no Minako (ハダカの美奈子)
- Originally a founding member of AKB48 and Team A, she was transferred to Team B for their debut, along with Urano Kazumi and Watanabe Shiho. She left AKB48 in 2012 as the result of a scandal involving her and Yonezawa Rumi.
- Of all the graduated members who ran in the AKB48 32nd Single General Election, Hirajima was the only one who ranked in the top 64.
- Her motto is; "Smile as much as possible." (できるだけ笑顔でいること)
- Her saying goes; "Do it when you can do it." (やる時はやる)
- Likes the anime Ojamajo Doremi.
- She likes collecting manga, books and teddy bears.
- Has said she doesn't admire any historical figures, the person she respects most is her father.
- Personality quizzes from MCs during Team B Stage One have revealed she will be an otaku in the future, and was a princess in a past life.
- Has had the nickname Nacchan since elementary school.
- Was the vice president of her student council in the first year of Junior High School.
- Wants to be an actress in the future.
- Admires Yonekura Ryoko because she's cute and can be a bad girl.
- If she could be born again, she'd like to be a boy.
- Likes science, but isn't so good at Math and English.
- Takes her own lunch to work, with a set given to her by Urano Kazumi.
- Wants to visit a transvestite bar.