2015–16: Base and She Is

On January 2, 2015, it was confirmed that Jonghyun would be making his solo debut on January 12, 2015, with his first mini album, Base.[15] Though the title track was originally the more upbeat "Crazy (Guilty Pleasure)", which Jonghyun wrote the lyrics to, the pre-released track "데자-부 (Déjà-Boo)" was named as a second title track after it charted incredibly well on the digital charts. Both of the tracks were featured. Déjà-Boo was co-composed by Jonghyun's close friend, Zion.T.[16] Jonghyun's debut mini album met much acclaim and drew attention not only because he participated heavily in the creation process, but because of the multiple collaborations with artists outside of S.M. Entertainment, including: rookie rapper Iron, Younha, Wheesung and Zion.T. The album ended up peaking at first place in its physical release on both the Billboard's World Album chart and the Gaon Album Chart.[17][18] On January 10, it was revealed that Jonghyun would be participating in Mnet's entertainment program 4 Things Show to promote his solo album. His appearance was not only marked as the first episode of the second season, but the first episode of the new year.[19] Taemin, Davichi's Minkyung and Zion.T appeared as Jonghyun's friends during the episode. Later on during the year, it was revealed that Jonghyun would be participating in the debut of the Mnet program, "Monthly Live Connection". The premise of the show revolves around bringing two artists together from different musical backgrounds to collaborate on a song. Jonghyun recorded the show in September, and the recording was edited into four episodes which aired in October. Jonghyun's collaboration partner for the show was soloist Jung Joon Young. In March 2015, Jonghyun both composed and wrote the song "Playboy", which was featured in EXO's second Korean album, "EXODUS".[20] A month later, in April 2015, Lim Kim released "No More" on her third mini album, "Simple Mind", which Jonghyun also composed and wrote. He participated in the vocal direction for all of the aforementioned as well.[21] In May 2015, he wrote the title track of Shinee's fourth Korean album, "Odd", "View", making it the second title track he had written for the group since their debut. He also wrote and composed the track "Odd Eye" on the same album, and the co-wrote the lyrics to the track, "Chocolate", on the repackage album released in August 2015.

In August 2015, Jonghyun held his first solo concert "The Story by Jonghyun" as a part of S.M. Entertainment's concert series "The Agit".[22] Jonghyun performed songs from his first mini-album, and also released a new compilation album for each of his songs that were recorded in his radio show. The compilation album, Story Op.1, was released on September 17, 2015.[23] Jonghyun did not promote the album on music shows, but did participate in three free busking concerts to promote it. Following the release of the album, Jonghyun performed a total of 12 sold-out shows, titled The Story by Jonghyun, at the SMTOWN Coex Artium SMTOWN Theatre from October 2–4, October 8–11, and October 16–18. Each concert featured a different guest, including Shinee′s Onew and Taemin, IU, Zion.T, Jung In, Lim Kim, Oksang Dalbit, Coffee Boy, Nine, Lee Ji Hyoung, Soran and poet Ha Sang Wook.[24]

Jonghyun also published a book in September. The book, titled "Skeleton Flower: Things That Have Been Released and Set Free," talks about the singer's songwriting experience and inspirations.[25] As of September 2015, the special corner has taken place four times in total with nine songs being released that were all either: completely written and composed by Jonghyun, or written by Jonghyun with the composition help of his composition group, WeFreaky.[26] In October 2015, Jonghyun was selected as one of the top five K-pop idol vocalists by a survey completed by 40 anonymous music industry officials.[27]

Jonghyun also composed and wrote the track "Already" for Taemin's first full-length solo album, "Press It", which was released in February 2016.[28] Jonghyun later composed and wrote a track called "Breathe" for Lee Hi's album Seoulite, which was released on March 2016.[29] The collaboration marked the first occasion that an artist from S.M. Entertainment had formally collaborated with an artist from YG Entertainment. Jonghyun released a collaboration single with Heritage titled "Your Voice" which is a medium tempo acoustic pop track. It was released on March 18, 2016, as part of S.M. Entertainment's SM Station project.[30] On May 24, 2016, S.M. Entertainment released Jonghyun's first studio album "She Is," consisting of nine tracks, and a music video for the title track "She Is." The album mainly contains songs written and composed by the artist himself.[31] "She Is" was described by Jonghyun as the album that "one can feel his passion as a singer-songwriter the most" and covers various genres such as electro-punk, EDM and R&B.[32]