Consisting of a combination of unusual interpretations of familiar musical instruments, textures both acoustic and electronically made, samples of recordings of people such as David Sylvian and Paul Bowles doing readings, and everyday sounds borrowed from field recordings of city streets, async has underlying themes of the worries of the end of life and the interaction of differing viewpoints in humanity.

Promoted with two art museum installations, a short film contest, and premiering via a listening event at Big Ears Festival, async was first released in Japan by Sakamoto's label Commmons in March 2017 before Milan distributed it to other nations in April 2017.

"[3] Inspired by the minimal structures of the works of Claude Debussy and the free jazz stylings of John Coltrane,[12] async, as Milan Records summarized, is a set of representations of Sakamoto's thinking that "plays with ideas of a-synchronism, prime numbers, chaos, quantum physics and the blurred lines of life and artificiality/noise and music.

"[6] Sakamoto conceived the album as the soundtrack for a nonexistent movie by Andrei Tarkovsky,[6] whose works mostly deal with mortality (see the Worries of death subsection of this article)[13] and employed walking scenes with the type of Foley featured on async.

[11] async employs a variety of sound-producing techniques, such as field recordings, making mist textures out of chorales, and wailing sounds from glass.

"[7] Sakamoto did the field recordings by walking through streets in New York City, Tokyo, Kyoto, and Paris with a cell phone microphone in his hand,[18][8] activity that made up for four months of the album's production.

[14] For "Walker," Sakamoto spent around ten to fifteen minutes recording his footsteps while walking in a forest filled with leaves, which makes up most of the track.

[27] This theme of async was compared by writer Karl Smith to the works of Shane Carruth, whose films also deal with chaos in human nature.

[28] Some critics noted Sakamoto's worries about death seeping into the album,[30][11] which were influenced not only by his experience with cancer but also the many earthquakes and tsunamis that occurred in Japan in 2011.

"[13] The recording was done in 2011 and was one of ten poem readings Sylvian submitted to Sakamoto for a charity concert supporting victims of the 2011 Tōhoku earthquake and tsunami.

[37] A follow-up to the installation, titled IS YOUR TIME, ran from December 9, 2017, to March 11, 2018, at NTT InterCommunication Center, and also featured music from async and visuals by Takatani.

[38] The first live performance of async in the United States was held in the Veterans Room at the Seventh Regiment Armory in the Upper East Side of New York City on April 26, 2017.

[42] From the approximately 800 entries that were submitted, In a Happy Place by Sikkim-based filmmaker Sandup Lepcha won the contest, receiving $3,000 and an opportunity to have Sakamoto compose for his next film.

[45][44] Mixmag gave async a ten-out-of-ten review, describing it as "full of church organs, hazy reverb, rippling synths and poetry about mortality and eternity, as well as Sakamoto’s distinctive piano, sonar bleeps and unforgettable melodies.

"[48] Lotus Land praised async as "yet another entry in his oeuvre which simultaneously feels unique from his other releases and yet inescapably Sakamoto in its depth and emotion.

called it "challenging and moving," highlighting its "unique ability to create genuine beauty with a varied — at times abrasive — palette" and the fact that Sakamoto "remains a radical after all these years.

"[47] As Paul Bowler summarized async, "Understandably ruminative in nature, it’s a renewed sense of creative vigour which provides the driving force on a piece of work which stands among the composer’s best.

[4] Andrew Ryce praised it for feeling "universal," where "anyone can pick up the objects around them and make music, and Sakamoto shows how engaging even the simplest exercises in sound can be.

"[9] However, Beta called them "striking inclusion[s],"[4] PopMatters critic Chris Ingalls felt they added "more layers of sonic curiosities,"[50] and Bowler described them as the album's "most oddly affecting" moments.

[74] Designed to be experienced asynchronously, the project diverges from traditional synchronization of sound and image reflecting Sakamoto's in an immersive experience.