She made debut as a solo artist on October 2, 2020.
Washio Reina was born on January 20, 1994, in Karatsu, Saga Prefecture, Japan.
Since kindergarten, she had the dream of becoming a singer. However, she did not have the confidence to sing in public and was a shy child. A changing point in her life was when she attended a concert of EXILE at Fukuoka Dome with her mother. Washio was so impressed by their performance that after learning an EXPG Studio would open in Fukuoka, she started attending it in her first year of high school. To be able to pay the fees of EXPG Fukuoka, she worked a part-time job in Karatsu. Washio dropped out from school after her first year of high school to focus on becoming a singer.
In 2011, after attending EXPG Fukuoka for two years, Washio participated in the vocal selection of the EXILE Presents VOCAL BATTLE AUDITION 3 ~For Girls~.
On July 26, during an E-Girls SHOW event in SHIBUYA-AX, it was revealed that Washio was one of the winners of the VOCAL BATTLE AUDITION 3 and was added to FLOWER as a vocalist. On that same day, she was also added as a member of E-girls, having a concurrent position between the group and FLOWER.
On October 12, she made debut with FLOWER with the single "Still".
On September 30, she left Flower with the group's disbandment.
On December 22, with the announcement of E-girls' disbandment set for around the end of 2020, it was revealed that Washio would be making solo debut.
On January 31, it was revealed that Washio would be singing the theme song of the movie Shousetsu no Kamisama, titled "Call Me Sick", and an insert song of the soundtrack, titled "Konna Sekai ni Shita no wa Dare da". It was also revealed that she would be using the stage name Rei (伶) for her solo activities.
On September 27, it was announced that she would sing the title song of an upcoming short film from the CINEMA FIGHTER franchise directed by Mori Yoshitaka and starring Nakatsuka Yuta.
On December 31, she left E-girls with the group's disbandment, now being active as a solo artist under the stage name Rei.
On March 23, Flower's YouTube channel was renamed for Rei to use it as as the official channel for her solo career. At the same time, it was revealed that there were plans for her to release song covers selected by herself, live streaming, as well as videos about her hobbies and private life.
Washio is an enthusiastic gamer. She often plays cooperative video games such as Fortnite and Call of Duty together with Sandaime J SOUL BROTHERS' ELLY, THE RAMPAGE's Suzuki Takahide and BALLISTIK BOYZ's Kainuma Ryusei. In June 2019 she traveled to California alongside ELLY to participate as a guest player in the Fortnite Summer Block Party, a Pro-Am gaming tournament. There, she teamed up with BELL of Japanese pro-gaming team CRAZY Raccoon.
- Main article: List:Washio Reina Discography Featured In
- Digital Singles
- Other Singles
- [2020.11.18] Shirayukihime - From THE FIRST TAKE
- Original Songs
-  Chiru Chiru Michiru (散る散る満ちる)
- [2013.08.14] DJ DECKSTREAM - DECKSTREAM.JP (#12 Ano Hi no Sayonara feat. Washio Reina (Flower / E-girls))
- [2014.03.26] m-flo - FUTURE IS WOW (#12 d.w.m / m-flo + Reina Washio (Flower / E-girls))
- [2018.06.20] MACO - BEST LOVE MACO (#3 Dear My Friend feat. Washio Reina (E-girls / Flower))
- [2018.xx.xx] JAY'ED & Washio Reina - UTA MONOGATARI -CINEMA FIGHTERS project- (Bonus CD) (How about your love?)
- Solo Songs
-  Hitohira
- For the list of songs Washio is credited as lyricist and composer in Flower, her own songs and for the artists featured in this wiki, see the Category:Songs written by Rei and Category:Songs composed by Washio Reina.
- Favorite artists: JUJU, Amuro Namie, Crystal Kay
- Favorite movies: Harry Potter, Meitantei Conan
- Favorite food: Nattou (Fermented soybeans)
- Favorite flower: Sunflowers
- Hobbies: Karaoke, Watching music videos, Gaming
- She is currently the only member to be vocally featured on all E-girls' a-side singles.
- She revealed on the TV show EG-style that one of her dreams is for E-girls do a dome tour and Flower do an arena tour.
- She started an Instagram account on July 27, 2017.
- Her fans gave her the nickname Rachel (れいちぇる). EXILE HIRO often calls Washio by the nickname Wasshi (わっしー).
- Former AKB48 member Maeda Atsuko revealed to be a fan of Washio and attended Flower's Flower LIVE TOUR 2015 "Hanadokei" on June 26 in Zepp Tokyo.
Oldest Member of E-girls
- 【鷲尾伶菜】鷲尾伶菜 ソロプロジェクト「伶」第一弾『Call Me Sick』が、映画「小説の神様 君としか描けない物語」の主題歌に決定!!
- 10/2(金)公開の映画『小説の神様 君としか描けない物語』主題歌・挿入歌 全6楽曲の連続配信が決定！
- E-girls 鷲尾伶菜ソロプロジェクト「伶」始動！ 2020年10月2日（金）劇場公開映画『小説の神様君としか描けない物語』主題歌＆挿入歌配信決定！
- FlowerのYouTubeチャンネルが伶YouTubeチャンネルとしてリニューアル 3/26（金）20時～ 伶「初めてのYouTube生配信！#0」決定！
- シネマファイターズ プロジェクト第4弾「昨日より赤く明日より青く-CINEMA FIGHTERS project-」主題歌情報
- 前田敦子、Flower鷲尾伶菜は「全てがどストライク」 豪華タッグに「最高の2人」の声