Taeyeon's vocal received positive feedback from the song's composer Park Hae-woon: "She fully understood the song in its entirety and expressed each detail very precisely..though this song requires the lowest note that a female singer can produce, Taeyeon executed them perfectly." In April 2012, a Girls' Generation subgroup named TTS was formed with Taeyeon and fellow members Tiffany and Seohyun.Their debut EP, Twinkle, met with much success and became South Korea's 8th highest selling album of the year.It peaked at number two on South Korea's Gaon Album Chart and its title track sold over one million digital copies.Her second extended play, Why (2016), charted at number one and yielded two Gaon Digital Chart top-ten singles "Starlight" and "Why".The album met with complimentary reviews, with Jeff Benjamin from Fuse praising Taeyeon's "powerful vocals" in it.With her accompanying concert series, Butterfly Kiss, she became the first Korean female solo artist to hold a full-scale concert while still being an active girl group member.During her second year in middle school, Taeyeon accompanied her father to SM Academy (a former music institution and auxiliary affiliation of S. During the next year, Taeyeon accompanied her father from their hometown to Seoul on every Sunday to receive her vocal lessons from The One.
The training process was so tough that it nearly made her quit at one point; she continued, however, and debuted as a member of girl group Girls’ Generation in August 2007.
This is a rather mature song, so I would be lying if I said I didn’t have my doubts, but she blew me away.
I was moved to tears listening to her singing." Following Taeyeon's working relationship with him from the drama Beethoven Virus (2008), musical director Lee Pil-ho was determined to collaborate with her again on his MBC's melodrama The King 2 Hearts (2012) soundtrack, by having her record the main theme song "Missing You Like Crazy".
Her other 2014 releases included "Colorful" for JTBC's campaign "The World Is More Beautiful Because We're Different" and "Love, That One Word" for the SBS's drama You're All Surrounded; the latter entered Top 10 on both Gaon Digital Chart and K-Pop Hot 100.
Taeyeon began working on a solo album in late 2014, believing her "right time" had come.