Written around a documentary theme, the band were inspired by personal and world events in 2011 to create material for the album.

The first single "Identity", a song originally written during that album's recording sessions, was released three months after Kikuuiki.

Originally, the album's documentary concept focused on themselves as a band, but the disaster prompted Yamaguchi to take inspiration from world events such as the earthquake.

"Bach no Senritsu o Yoru ni Kiita Sei Desu", released as the album's third single in July, was written as therapy for Yamaguchi during this time.

The band began work on the song "Endless", and continued to develop it over the course of eight months, however due to Yamaguchi's dissatisfaction with the piece.

Yamaguchi spent much of this time writing lyrics that would express 2011 as a concept, and entrusted the album's arrangement to the other band members.

[4] In order for the band to sell more and become more well known, Yamaguchi felt that Sakanaction should utilize new techniques to promote themselves, such as appearing more in media and on television.

[14] The documentary theme for the album was fully conceptualized in January, during the "Rookie" and early "Endless" recording sessions,[6] developed from Yamaguchi's feelings of wanting to express himself more.

The third package compiled both concerts and added a third DVD, Sakanaquarium 2010 (D), featuring tour documentary and interview footage.

Instead of merely adopting it as a theme, Sakanaction decided to record an actual documentary of the album's creation process, on an additional visual media disc.

[6] Just prior to "Rookie"'s physical single release, Japan experienced the 2011 Tōhoku earthquake and tsunami on March 11, 2011.

[4] In April, Yamaguchi visited Kesennuma and Minamisanriku in Miyagi Prefecture to help with the emergency relief, without a media presence.

[6] Yamaguchi wrote the songs "Bach no Senritsu o Yoru ni Kiita Sei Desu" and "Years" directly after the earthquake, as therapy for himself.

[20] Yamaguchi felt inspired to create music that when listened to strongly expressed the sentiments of a certain era, which he saw in the music of John Lennon, Bob Dylan and in Japanese singer Yōsui Inoue's song "Kasa ga Nai" (1972);[21] as a way for people in the future to be able to experience how people felt during the post-earthquake era.

[23][24] This made Yamaguchi feel as if he was the director of the project, with drummer Keiichi Ejima leading the band as its captain during his absences as he focused on lyric writing.

[23] In addition to the band members, Yamaguchi felt that Sakanaction had gained a solid core of peripheral staff that helped with the recording process, compared to their previous albums.

[17] In contrast to Kikuuiki, which left him emotionally drained, he felt optimistic after completing Documentaly, feeling that he had a future in music.

[23] Yamaguchi stressed dynamism during the writing process, choosing a non-standard pop song structure for the piece.

[17] Seeing releasing music as an act of self-expression, "Endless" was a song written by Yamaguchi to express his inner feelings as directly as possible.

[17] He wrote the songs as having a common theme spread across two works, hence featuring them on Documentaly in the same order as they had appeared on the "Bach no Senritsu o Yoru ni Kiita Sei Desu" single.

[45] The song's music video, co-directed by Takumi Shiga and the band's long-time creative consultant Hisashi "Momo" Kitazawa, was unveiled on YouTube on the day of the album's release.

[49] On September 8, 2011, Yamaguchi threw the ceremonial first pitch for the baseball match between the Yomiuri Giants and Chunichi Dragons.

[55] Kenta Eizumi of Vibe felt that Sakanaction expressed a strong sense of crisis happening in the contemporary Japanese music business on the album.

[56] Looking at the album's central track "Endless", Shimizu felt that the song was an ambitious "compilation-like work", likening it to electronic musician Rei Harakami.

[36] They described "Monochrome Tokyo" as an "impressive rock number created by synthesizer and bass guitar riffs", praising the band's skill at removing musical elements as well as Yamaguchi's "emotionally sung" and "sexy" vocals.

[36] For "Antares to Hari", the reviewers felt that a "stylish jazz funk aroma" was created by a "relaxed" bass line and guitar cutting, and praised the light atmosphere created by the deep synths, while "Ryūsen"'s "comfortable" acoustic guitar "paints a dramatic and grand scene.

[36] The reviewers likened "Kamen to Machi" to Japanese electronic band Yellow Magic Orchestra, and felt a sense of tension created by Yamaguchi's fast-tempo vocals and the changing background instrumental.

[36] They believed that the album's closing song "Document" was a condensation of the album's taste, and that the final lyric "ai no uta utatte mo ii kana tte omoihajimeteru" (愛の歌 歌ってもいいかなって想い始めてる, "I'm starting to think that it's okay to sing love songs") set to a "relaxed and hopeful sound" had a powerfully lingering impression.

[61][62] The third single, "Bach no Senritsu o Yoru ni Kiita Sei Desu", was praised for its "ecstatic beat" and "elegant piano",[63] and "smart dance music" sense.

[65] Reviewing the single's B-side "Years", CDJournal felt that it was an "ambient-taste electro song that develops through its triple metre," and praised Yamaguchi's lyrics as "hopeful" and "poignant".