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Yui was born in Fukuoka, Japan. She grew up in a single-parent family; her father left her mother before she was born. She stated that she had always been close to music; she would remember the beats from music she heard on the radio, and could sing it. By the time she was in elementary school she thought she would like to become a singer. During her third year in middle school, at her mother's suggestion, Yui began writing a journal of her feelings and tried to compose them into poems. By the time she was in high school, she began to write songs. While in high school, she worked part-time to help pay for tuition. She thought that, being so busy, she no longer had the time to realize her dreams of a music career. Eventually she got ill. While in hospital, she was overwhelmed with the desire to make music. She decided that school and music could not coexist. Upon leaving the hospital, she encountered a live street performance and expressed her desire to pursue a musical career to the band, Bianco Nero, at the end of the concert. Bianco Nero advised Yui to join a private music school. Yui soon dropped out of high school and began to study guitar and songwriting at a juku in her hometown of Fukuoka. Aspiring to become a professional, she took to street performing at Fukuoka's Tenjin Station. These street performances helped Yui to overcome her shyness.