Yui Kobayashi (Japanese: 小林 由依, Hepburn: Kobayashi Yui; born 23 October 1999), also known as Yousti (stylized in all lowercase), is a Japanese singer and model. She is a former member of the idol group Sakurazaka46 (formerly Keyakizaka46). She is represented by Sony Music Records and is an exclusive model with a fashion magazine with.
On August 21, 2015, Kobayashi along with 22 other members was announced for the newly created idol group Toriizaka46, later renamed to Keyakizaka46 and currently known as Sakurazaka46. Kobayashi made her musical debut with Keyakizaka46's first single, Silent Majority. In October of the same year, Kobayashi made her runway debut at the GirlsAward 2016 Autumn/Winter fashion show.
As of 2019, Kobayashi has made an appearance in all Keyakizaka46 singles. She formed a duo named "Yui-chans" (ゆいちゃんず, Yuichanzu) with Yui Imaizumi, first appearing in Silent Majority with the song "Shibugakawa". With Imaizumi's graduation in 2018, Kobayashi and Mizuho Habu formed another duo named "Senko Shimai" (線香姉妹), appearing in Ambivalent with "302-Goshitsu". She held performance center roles typically held by Yurina Hirate when Hirate was unavailable, including the 60th Japan Record Awards and the 69th NHK Kōhaku Uta Gassen.
Kobayashi became an exclusive model for fashion magazine with on July 27, 2018. On March 13, 2019, she released a photo-book titled Kanjō no Kōzu (感情の構図), published by Kadokawa.
Kobayashi's first independent acting role was in the 2020 live-action adaptation of Wasteful Days of High School Girls by TV Asahi. She played the role of Lily Someya, a multiracial transfer student; Kobayashi dyed her hair blonde for the role. She will appear in Sakura, an upcoming movie to be released on 13 November 2020.
On November 29, 2023, Kobayashi announced that she would be leaving Sakurazaka46 after her graduation concert on January 31–February 1, 2024 at the Yoyogi National Stadium.
2025–present: Solo career as Yousti
In May 2025, Kobayashi announced her upcoming debut as a solo singer under the name Yousti. The stage name is a combination of her name and "ostrich", as she wished that her music could be a temporary "escape from reality" for those facing hardships (based on the common misconception that ostriches bury their heads in sand to avoid danger). Her official fandom name is "Aisti", a combination of "love" (愛, ai), the English superlative degree suffix "st", and the English "I". Her first self-titled EP was released on August 27.
Yui Kobayashi's page on Keyakizaka46's website