"Deepness" was released close to five months after Misia's previous single, "Koi wa Owaranai Zutto". It is the first of two back-to-back singles, both servicing the soundtracks of two installments of the Ōoku franchise. It was released digitally in truetone format on October 12, 2012. The first pressing of the physical release came in digipak format and included the password to a secret Ustream broadcast of a mini concert held on December 19, 2012 to celebrate the release of the single. The single features the B-side "Koi Gram", written by Satoshi Shimano, as well as two remixes by DJ Gomi of the title track and of Misia's rendition of Michael Jackson's "Heal the World".
Composition
"Deepness" is written in the key of B minor and set to a common time tempo of 77 beats per minute. Misia's vocals span from A3 to E5. "Deepness" was written specifically for Ōoku: Tanjō. Before writing the song, Misia brushed up on the world of Ōoku by reading the original manga in its entirety. She was struck by the female shōgun and all-male ōoku, and felt that the reversal of gender roles depicted in the manga was something modern women could relate to. Misia decided to write lyrics that revolved around the dedication of the ōoku and the outpouring of love for their one and only shōgun.
Critical reception
EMTG Music's Yūichi Hirayama stated about "Deepness" that "the message is in the sound of the song itself" and compared it to the "crisp" sound of Misia's "Snow Song". Hirayama described the song as being the "ideal vehicle" for Misia's voice. He also praised Phil Tan for his work mixing the track. CDJournal critics said the song was reminiscent of an Alicia Keys mid-tempo ballad and also praised Tan's contribution. They described "Deepness" as "epic" but not too overwhelming so as to not put it on repeat.
Music video
The music video for "Deepness" was directed by Sayaka Nakane and shot in early October 2012 in the Mongolian grassland. The video took four days to shoot to completion.
Chart performance
"Deepness" made its chart debut on the weekly RecoChoku truetones chart at number 15. The song dropped six spots, down to number 21, on its second week. It moved up twelve spots to number 9 on its third week. On its fourth week, "Deepness" slid up one spot to number 8. The song peaked on the truetones chart at number 6 the following week. "Deepness" debuted on the weekly RecoChoku singles chart at number 2, blocked from the top spot by Kana Nishino's record-breaking single "Always". "Deepness" entered the daily Oricon Singles Chart at number 14 and peaked at number 11. The single debuted at number 15 on the weekly Oricon Singles Chart, with 5,000 copies sold. It charted for ten consecutive weeks and sold a reported total of 12,000 copies during its run. "Deepness" peaked at number 10 on the Billboard JapanHot 100, making it Misia's seventh top ten entry on the chart.
