- Name: Sayashi Riho (鞘師里保)
- Nickname: Rihoriho (りほりほ), Yasshi (やっしー), Sayasshi (さやっしー)
- Birthdate: May 28, 1998
- Birthplace: Higashihiroshima, Hiroshima, Japan
- Blood Type: AB
- Height: 155cm
- Hobbies: Listening to music, sleeping
- Specialties: Calligraphy, giving massages
- Favorite Food: Peach, chicken wings, sushi, oysters
- Least Favorite Food: Carrot
- Favorite Color: Pink, white, black, yellow-green
- Dislikes: History
- Looks Up To: Takahashi Ai, Suzuki Airi
- Hello! Project groups:
The ninth generation made their official presentation on the same day they were announced as new members in Hello! Project 2011 WINTER ~Kangei Shinsen Matsuri~ concert, and they participated in the songs: "Aozora ga Itsumademo Tsuzuku You na Mirai de Are!" and "Tomo".
On the 29th of October 2015, Sayashi Riho announced that she would graduate from the group at the end of the year. She intends to travel abroad and study English. The planned graduation took place on the 31st of December during H!P's New Year's Eve concert, "Hello! Project COUNTDOWN PARTY 2015 ~ GOOD BYE & HELLO ! ~.".
In November of 2018, her contract with UP-FRONT ended. However, in March of 2019, Sayashi is scheduled to appear as a special guest at Hello! Project 20th Anniversary!! Hello! Project Hina Fes 2019. This will be Sayashi's first public appearance since her graduation in 2015.
In 2019, Sayashi became a touring member of BABYMETAL, including their performance at Glastonbury Festival 2019.
Since July 10, 2020, Sayashi has her own column called "RihoColumn" (りほこら(む)) in the online magazine NewsCrunch, published by Wani Books. On September 3rd, she announced that she had signed to Japan Music Entertainment as a solo artist.
- [2011.08.31] Sayashi Riho~Greeting~ (さやし りほ～Greeting～)
- [2012.03.09] RIHO
- [2012.09.26] HyaaHo~i♪( ´θ｀)ノ (ひゃっっほ〜い♪( ´θ｀)ノ)
- [2013.03.28] snowdrop
- [2014.03.12] Riho's Fashion Archive
- [2015.04.08] Sixteen
- [2011.08.27] Sayashi Riho (さやしりほ)
- [2012.08.27] Un Deux Trois (アンドゥトゥア)
- [2013.11.25] Taiyou (太陽)
- [2015.03.25] Juurokusai (十六歳)
- [2015.12.25] Morning Musume '15 Sayashi Riho Collection 2011-2015 (モーニング娘。’15 鞘師里保全集 2011-2015)
- [2016.03.12] 17sai no Ketsudan (17歳の決断; A 17 Year Olds Decision]]
-  Sharehouse (シェアハウス)
- TV Dramas
-  Suugaku♥Joushi Gakuen (数学♥女子学園)
- TV Programs
-  Bijo Gaku (美女学)
- [2011-2012] HELLOPRO! TIME (ハロプロ！ＴＩＭＥ)
- [2012-2013] Hello! SATOYAMA Life (ハロー！ＳＡＴＯＹＡＭＡライフ)
- [2014–2015] The Girls Live
-  UstreaMusume
-  Michishige Sayumi no "Mobekimasutte Nani??" (道重さゆみの『モベキマスってなに？？』)
- [2013–2015] Hello! Station (ハロ!ステ)
-  Fashionable (ファッショナブル)
-  Reborn ~Inochi no Audition~ (リボーン～命のオーディション～) (as William Shakespeare)
-  Stacy's Shoujo Saisatsu Kageki (ステーシーズ 少女再殺歌劇)
-  Idol Nihonryuu ~Onna Nichibu~ (アイドル日本流～おんな日舞～)
-  Gogaku Yuu (ごがくゆう)
-  LILIUM -Lilium Shoujo Junketsu Kageki- (LILIUM －リリウム 少女純潔歌劇－)
-  TRIANGLE -Trine Angle- (TRIANGLE -トラインアングル-)
-  35MM: A MUSICAL EXHIBITION
- [2011–2015] RIHO-DELI (on Sundays)
- [2012–2015] Morning Musume no Morning Jogakuin ~Houkago Meeting~ (モーニング娘。のモーニング女学院～放課後ミーティング～)
- [2014–2015] Young Town (ヤングタウン)
- Her official Morning Musume image color is red.
- Her catchphrase is "Hyahhhooi♪" (ひゃっっほーい♪( ´θ｀)ノ～), complete with the emoji, and she uses it to begin her blog posts.
- Her favorite drink is cider, to which she has associated the catchphrase "shuwashuwa pon!" (しゅわしゅわぽん！).
- She was formerly a student at the performance arts school Actor's School Hiroshima.
- She has been dancing since she was six years old.
- Has a little brother and a little sister.
- She and Suzuki Kanon are the first members of Morning Musume that were born after the group's formation in 1997.
- At school, she likes lunchtime.
- Has been told she was good at dancing since she was young.
- She enjoys wearing frilly skirts.
- Her motto is "Whatever doesn't kill us makes us stronger".
- Her favorite phrase is "Once-in-a-lifetime encounter".
- Is one of three Morning Musume members to have the blood type AB, along with Kago Ai and Kamei Eri.
- Noted her favorite Morning Musume song to be "Nanchatte Ren'ai" in a 2011 magazine interview, and "Kimagure Princess" in a 2012 interview.
- Niigaki Risa refers to her as Yasushi (ヤすシ), coined from when Tsunku accidentally misspelled Yasshi (ヤッシー).
- Has been remembered for having a complicated name, due to the difficulty and rarity of the kanji for Saya (「鞘」).