Kikuuiki (Mixing Airspace; stylized as kikUUiki, Japanese pronunciation: [ki̥kɯꜜːiki]) is the fourth studio album by Japanese band Sakanaction. It was released on March 17, 2010, through Victor Entertainment. In January, the album was preceded by the single "Aruku Around", which was met with the greatest commercial success for the band since their debut, reaching number three on Oricon's singles chart. The album was nominated as one of the finalists for the CD Shop Awards, and was lauded by critics for its cohesive sound and literary lyrics. At the time of release, it was their most commercially successful release since their debut, reaching number three in Japan.

Sakanaction spent most of 2009 experimenting on the album's single "Aruku Around", followed by two months of recording in January and February 2010. Most of the final recording stages were spent on the song "Me ga Aku Aiiro", a seven-minute rock opera used as a promotional single during its release. The album saw a new recording approach for the band, where the members worked more spontaneously and synchronized. The album was influenced by the commercial success of "Aruku Around", and was written as a response to the song.

After recording two studio albums in Sapporo, the band moved to Tokyo in spring 2009 to further their musical potential. Their first album produced in Tokyo, Shin-shiro (2009), saw a new approach for the band, where vocalist Ichiro Yamaguchi asked the other members of Sakanaction to arrange songs individually, instead of together. Led by the singles "Sen to Rei" and "Native Dancer", the album became their most commercially successful in their career, peaking at number eight on Oricon's album chart. Despite this, Yamaguchi was disappointed with the sales, and was not sure why the album stalled at 30,000 copies sold.

After the release of the album in January 2009, Sakanaction performed a two-month tour of Japan, Sakanaquarium 2009: Shinshiro. This was followed by appearances at many summer music festivals, including Sweet Love Shower, Nano-Mugen Fes, Rock in Japan and Rising Sun Rock Festival. On June 13, 2009, Sakanaction performed at Version 21.1, a newly created rock event by Sakanaction and the rock bands Ogre You Asshole and the Telephones to showcase rock music of the 2010s. On October 10, Sakanaction performed their first overseas concert, the Gentra X Ssamzie Sound Festival in Paju, South Korea.

Yamaguchi had started collecting ideas for Kikuuiki in February 2009, less than a month after the release of Shin-shiro. The band spent most of 2009 experimenting on the song "Aruku Around", and performed the song at their summer festival appearances at Rock in Japan and Rising Sun Rock Festival, to see how the audience would react to the song's different approach. After "Aruku Around" was released as a single in January 2010, it became a commercial and critical success. It reached number three on Oricon's single charts, and was praised for its strong arrangement and Yamaguchi's poetic lyrics. The single's success surprised the band, who never considered it could become as popular as it did.

The album was primarily recorded at Freedom Studio in Shinjuku, Tokyo, with secondary recording sessions held at Sound Arts, Avaco Creative Studio and Galva Studio, all in Tokyo, as well as Studio Wakefield in Tama-ku, Kawasaki. Recording sessions for "Aruku Around" were held in 2009, while the bulk of the album was recorded in January and February 2010. The recording sessions finished on February 16, a month before the album's release date. The writing process took longer than expected and the band had to postpone the album four times from their intended finishing date, mostly due to the complexities of recording the seven minute long song "Me ga Aku Aiiro".

The Kikuuiki album sessions were influenced by the commercial success of "Aruku Around", where the band considered what sorts of songs they wanted to make, and what sort of music they should present to their new audience for the audience to understand what songs Sakanaction create other than "Aruku Around"-style ones. The band did not want to make an album full of songs identical to "Aruku Around", and instead wanted to express to their listeners the breadth of musical inspirations that they could mix together. Yamaguchi felt that it was important to not release a second similar song immediately after "Aruku Around", as he saw that music consumers in the 2010s were acting as critics on their own Mixi or Twitter accounts. For these people, he believed it was important to exhibit different aspects of the band. He felt this was important for growing Sakanaction as a band, to break the cycle of a musical act becoming popular, then continuing to release the same style of music that made them popular until people grew tired of them. Even before the single's success, the band planned to feature songs on the album that would go against listeners expectations of what Sakanaction was as a band. On the other hand, the band attempted to keep a commercial sound, the same goal of Shin-shiro, or else they felt that their efforts would have been wasted. This led the band trying to create pop art music, blending art with commercialism.

The creation process for Kikuuiki was different to that of Shin-shiro, where each member worked alongside Yamaguchi in a two-person meeting, and later working on the songs together as a band. For Kikuuiki, Yamaguchi recorded each song's demo, then in a meeting the band would discuss the song's feel and emotions, listing everything on a white board. Yamaguchi would then leave the other four band members to work on the song together, while he worked on their next song. Afterwards, he would return to the studio and make suggestions on their progress on the first song. This meant that Yamaguchi had less input on Kikuuiki than on the band's previous albums, which made him feel more like the band's producer. The lessened input made Yamaguchi feel that he had come to trust each member's musical abilities much more than before. On previous albums, the members needed to compromise or give up on ideas that they had, however on Kikuuiki they found that they understood each other much better. This led to the members expressing themselves more, such as drummer Keiichi Ejima, who showcased his taste in rock music strongly in the sound he created for the album. Many songs were still being created when they were recording, unlike previous albums where songs were entirely finished before recording the final take. This meant that many spontaneous ideas were included on the album. An example of this was the band wanted to add a chorus, they collected together all the people who happened to be in the studio at the time, including their musical director. The spontaneous process led to the song "Klee", written about the paintings of Swiss-German painter Paul Klee, to be recorded in a single take. Similarly, the song "Coelacanth to Boku" was inspired by the atmosphere of Yamaguchi's room as the album was being created. Instead of featuring repeating sounds on the album, Sakanaction decided to carefully consider how each sound-effect effected the song, and included very few repeating sounds.