Career
She is the General Manager of the AKB48 Group. Yokoyama"s first attempt to join AKB48 or a sister group was for SKE48"s second generation, but her audition was unsuccessful. She later passed the auditions with AKB48, and became a ninth-generation kenkyusei (trainee) member on September 20, 2009.
In 2011, she secured her first participation on an AKB48 single title track by placing 19th in the AKB48 general elections.
Her first A-side single was "Flying Get". In 2012, she placed 15th in the AKB48 general elections.
In the AKB48 Tokyo Dome Concert in 2012, it was announced that Yokoyama would join NMB48 and therefore hold a concurrent position between AKB48"s Team A and NMB48. In the same year in November, she sang on the A-side for NMB48"s sixth single "Kitagawa Kenji".
In 2013, she placed 13th in the AKB48 general election and third in its rock-paper-scissors tournament.
On April 28, 2013, NMB48 revoked her concurrency and she remained in AKB48. On December 8, 2014, it was revealed that Yokoyama would succeed Minami Takahashi"s job as the General Director of AKB48 after Takahashi"s leaving. With the graduation of Minami Takahashi scheduled for April 8, 2016, Yui becomes the current "Soukantoku" on December 8, 2015 during 10th anniversary stage of AKB48 Theater.
Variety shows AKBingo! Naruhodo High School NMB Genin!!.