Aimer teamed up with the "Agehasprings" group, which has worked with, produced, or provided music for various artists, including Yuki, Mika Nakashima, Flumpool, Superfly, Yuzu, and Genki Rockets. In 2011, her musical career began in earnest. In May 2011, they released the concept album Your favorite things. It covered numerous popular works, including works in various genre such as jazz and country western music. The number 1 record cover was based on Lady Gaga's "Poker Face", and was the first song to appear in the lead album chart for the jazz category in the iTunes Store. The album reached number 2.
On September 7, 2011, she debuted for Defstar Records, with the song "Rokutousei no Yoru", which was selected by Fuji TV as the ending theme of the 2011 anime series No. 6. "Rokutousei no Yoru" recorded its highest ranking at number 9 on the Rekochoku music distribution chart. The second single was released on December 14, 2011. "Re:pray/ Sabishikute Nemurenai Yoru wa" reached number 1 in the "Mora" music download charts site. The song "Re: pray" was chosen as the 29th ending theme for the anime Bleach. The single includes a cover of Lady Gaga's "Poker Face". The song was previously featured in Aimer's Your Favorite Things, a cover album that was released during her indie era.
On February 22, 2012, she released her third single, "Yuki no Furumachi/Fuyu no Diamond", which had the theme of "winter" on all tracks. On May 11, 2012, Aimer released a digital single called "Hoshikuzu Venus". This single was intended to be the theme song and background music for Sasaki Nozomi's drama, Koi nante Zeitaku ga Watashi ni Ochite Kuru no daro ka?. This drama aired in April 16, 2012. On August 15, Aimer released her fourth single, "Anata ni Deawanakereba: Kasetsu Toka / Hoshikuzu Venus", which included a cover of Neil Sedaka's "Breaking Up Is Hard To Do". The first track of this single "Anata ni Deawanakereba: Kasetsu Toka" is an ending song of Fuji TV's anime series Natsuyuki Rendezvous.
On March 20, 2013, Aimer released the single "RE:I AM", which was used as the ending theme for the penultimate episode of Mobile Suit Gundam Unicorn. According to an interview, the song title "is an anagram of [her] name (Aimer), and has the meaning of breaking down a word and constructing it into another." Aimer's eighth single, "Brave Shine", appeared as the second opening theme to the Fate/stay night: Unlimited Blade Works anime, and was released on June 3, 2015. Another song, "LAST STARDUST", which was also a candidate for the opening, appears as an insert song in episode #20.
On August 18, 2016, Aimer announced her special 4th studio album "daydream" to be released on September 21 that features collaboration songs between her and popular artists such as Taka (ONE OK ROCK), Yojiro Noda (RADWIMPS), TK (Ling tosite sigure), chelly (EGOIST), Takahito Uchisawa (androp), Hiroyuki Sawano, Sukima Switch, and Mao Abe. Taka additionally produced four new songs for this album, while TK provided two. Also includes the ending theme of "Kabaneri of the Iron Fortress (anime)" made in collaboration with chelly (EGOIST) and Hiroyuki Sawano and more for 13 tracks total. The album was released in three versions: a limited CD+Blu-ray (Type-A), a limited CD+DVD edition (Type-B), and a regular CD only edition. The song "Falling Alone" was used as lead track and was previously released as her 10th digital single as advance of the album.
On August 20, 2016 Aimer revealed her face for the first time on Music Station with the song Chouchou Musubi. Following the announcement of her 4th album daydream, Aimer performed the ending song to the Season 5 of anime series Natsume's Book of Friends, "Akane Sasu."
On January 5, 2017 it was announced that Aimer wrote a song for the Japanese culinary exhibition "Tabegamisama no Fushigina Resutoranten" directed by the multimedia entertainment studio Moment Factory. A day after it was revealed on Aimer's official Twitter profile that the name of the song for the exhibition would be "Kachō Fūgetsu". Later, it was also revealed another single, which would be used as opening theme for the Japanese drama Ubai ai, fuyu, titled Kogoesōna Kisetsu Kara, and would be released on February 10, 2017. Successively, it was announced the release date, May 3, 2017, for two compilations containing Aimer's most famous songs, BEST SELECTION "blanc" and "noir". In the compilations there would also be included the two new singles, besides many songs from her previous albums.