"Passion" is a song recorded by Japanese-American singer-songwriter Hikaru Utada, taken as the fourth single from their studio album Ultra Blue (2006). It was released on December 14, 2005, in two physical formats and via digital download, distributed by EMI Japan and EastWorld. "Passion", alongside its English counterpart "Sanctuary", were used as the theme songs to the Square Enix video game Kingdom Hearts II (2005). The tracks serve as successors to "Hikari" and its English counterpart, "Simple and Clean", the themes of Kingdom Hearts (2002).

The creator of the Kingdom Hearts franchise, Tetsuya Nomura, sought to collaborate with Utada again as they had previously written "Hikari", alongside his prospects for them to break into foreign and international markets. The conception of the two tracks were to emphasize a "dusk"-like vibe to the game, in comparison to "Hikari" which they described as the "dawn". Musically, "Passion" has been described by music commentators as a multi-genre tune, noting elements of alternative rock, ambient and "ethereal" music. The song's lyrics delve into themes of nostalgia and discusses the circumstances of past, present and future.

Upon its release, both songs received critical acclaim, with critics praising Utada's improved production and vocals. Additionally, several publications ranked the songs on their year-end lists of 2005–06 and soundtrack lists. Commercially, "Passion" was successful in Japan, peaking inside the top ten on the Oricon Singles Chart and TBS's Count Down TV chart; despite this, "Passion"'s sales were much lower than previous releases. However, it was certified Gold in three categories by the Recording Industry Association of Japan (RIAJ).

An accompanying music video was directed in China by Utada's then-husband Kazuaki Kiriya, which depicts Utada in a dreamscape filled with animated clouds, figures and a cathedral-like architecture. The clip was inspired by numerous anime films and aesthetics, along with the atmosphere portrayed in Kingdom Hearts II. The music video for "Passion" was generally well received, but critics questioned the lack of footage from the video game. In order to promote the single, Utada performed the tracks on television shows such as Music Station and Hey! Hey! Hey! Music Champ, as well as part of their Utada: In the Flesh 2010 concert tour. Since its release, "Passion" and "Sanctuary" have been widely considered as two of the best songs in video game history and recognized as a major factor in Utada's commercial rise in the western market.

Background and conception In early 2003, The Walt Disney Company and Square Enix confirmed the sequel to Kingdom Hearts (2002). Regarding the theme song, Nomura only had Utada in mind as he felt they were a part of the franchise's family, and felt that their music could break into both foreign and international markets. But scheduling time with Nomura proved to be difficult, as Utada worked on their second English language album Exodus in their hometown New York City; they had been signed to Island Def Jam the previous year as their headquarters discovered their success in Japan.

Kingdom Hearts II was publicly announced in July 2005, and Nomura confirmed Utada's second involvement with the series, "When we were creating the original game, there were a lot of factors that were influenced by Utada-san's theme song. That influence will once again be felt in [our development of] Kingdom Hearts II ..." Nomura's second reason for choosing Utada over another singer was because he noted that fans from the first Kingdom Hearts associated them with the franchise. Utada derived their inspiration for the song's concept and connection with the game from the worlds and characters in Kingdom Hearts, and received in-depth explanations and clues from Nomura. Nomura also noted that Utada's previous theme song "Hikari" influenced several factors in creating the games.

Writing and recording "Passion" and "Sanctuary" were already written by Utada prior to the game's release, but they re-wrote certain aspects in order to represent elements of the game. Utada noted the game's visual aesthetics and storyline as a major influence towards the songwriting, and that the finished versions would lead up to the ending version of the track—which appears during the credits of the video. Utada made their second song appearance in Kingdom Hearts II as they felt the experience was better than "Hikari", which they believed was difficult to accomplish because of the "soulless vibe" the game has portrayed; though they believed the visual appearance was "crucial", the singer based their thinking process on the characters personalities instead. In a special interview with Oricon Style in December 2005, Utada talked about the process:

Utada first completed the English lyrics to "Sanctuary", as they said that they found it difficult to write the Japanese lyrics for "Passion". Retrospectively, Utada stated to Oricon Style that both of the songs' lyrics were some of their favorite lyrics to date. Knowing that the CDs of the single would be insufficient with the lack of additional material, they decided to create a B-side track that was identical to the first song; this was titled the "After the Battle" version, the composition played during the credits of the game. They traveled to West Hollywood, California, to record their vocals at Westlake Audio Studios with Pat Woodward, whilst the Japanese version was recorded at Bunkamura Studios, Shibuya, Tokyo with Matsui Atushi. Additionally, they re-recorded their vocals for the "After the Battle" version in order to blend it with its new arrangement. The tracks were produced by Utada, with additional production credits to Akira Miyake and Teruzane Utada.

Composition

"Passion" is composed as a multi-genre tune that emphasizes the core elements of alternative rock, ambient and ethereal music. MuuMuse's Bradley Stern asserted that "Passion" was Utada's "most complex" recording, noting the use of "passionate drumming" and ambient sounds. He described Utada's vocals as having an "ethereal"-like vibe. David Jeffries of AllMusic compared it to "A Whole New World" and the work of Nine Inch Nails. With instrumentation of drums, keyboards, electric guitars and synthesizers, the track was distinctive for its overuse of echoing throughout the composition. Additionally, critics noticed the overlapping technique of Utada's singing, along with the use of reversing certain sections of their voice to hide messages within the song.

The recording is composed in the key note of F♯ major, and is set in time signature of common time with a tempo of 109 beats per minute, whilst its chord progression develops in the sequence of B♭m7–Dm7–B♭m7–Dm7–Dm7–Dm. "Passion"'s lyrics delve into themes of nostalgia, and discuss the circumstances of past, present and future, which Utada noted was relatable to the characters in the game. However, Yahoo! Music's Miko Amaranthine said "Passion" is "another love song that resembles a missing love but leaving life without him/her." Furthermore, "Passion", "expresses moments of nostalgic childhood memories that either fold or, sometimes intertwine" and eventually introduces a "new world". A member at Channel-Ai stated that the theme encompassed the parent album Ultra Blue, but highlighted on "hope" more than "sadness". Vibes Mio Yamada said that the lyrics, "expressed weakness and strength simultaneously," and that the material was more mature than Utada's previous work.

Executive producers for Kingdom Hearts and head composer Yoko Shimomura said that the track needed to be more dramatic for the remaining of the accompanying score. In order to adapt to the remaining material on the soundtrack, Japanese musician Kaoru Wada arranged an orchestral version of "Sanctuary" that was performed by the New Japan Philharmonic Orchestra, which included the instrumentation of trumpets, several string sections and percussion.

Release "Passion" premiered on December 14, 2005, in two physical formats and for digital consumption, distributed by EMI Japan and EastWorld. Subsequently, the single and its B-side "Passion" (After the Battle) were included on the Kingdom Hearts II soundtrack; the video game that also included the single as its theme song was issued on December 22 that same year. Global distributions of the CD single commenced on December 26, whilst South East Asian editions were made available in stores on December 28. The DVD version came with the music video, alongside an Obi strip. The cover art was photographed by Mitsuo Shindo, who was alongside Utada's then husband Kazuaki Kiriya when shooting the clip; it depicts Utada in a vast corn field, which appears at the end. Various versions of "Passion"—such as the opening version, ending edit and orchestral instrumental—have been issued on three of the Kingdom Hearts soundtracks, including the Original Soundtrack Complete box set, and its special 10th anniversary edition. The single was also included on the soundtracks for the "remix" versions of the games, but "Sanctuary" served as its official theme song under their Western name Utada.

"Sanctuary" did not premiere in North America until March 28, 2006, with the video game, along with an end-September date in Australasia and Europe. Furthermore, EMI Music Japan distributed two versions of "Sanctuary"—the album edit and the "After the Battle" version— in Japan as a promotional single on January 1, 2009, through iTunes Store. On July 20, Island Def Jam premiered the track through radio stations in Japan, and subsequently served the album edit as the second single from their English album This Is the One (2009) two days later; only the North American editions feature the single. "Passion" and "Sanctuary" have appeared on compilation albums conducted by Utada, such as the Utada Hikaru Single Collection Vol. 2 (Nov 2010) and Utada the Best (Nov 2010).

Critical response Both songs received general acclaim from music critics. An editor of CD Journal praised the production, calling it "impressive". The reviewer praised the composition, stating that the sound as a "fantastic atmosphere" and their vocals as "beautiful". A reviewer from Channel-Ai gave "Passion" four-and-a-half stars out of five, but favored the track over "Sanctuary". For future releases, the reviewer also recommended Utada's Japanese counterparts over English dubs. Lex from VGMO.com gave the song eight stars, commending the production and sound. However, she said that she found "Passion" more "satisfying" than Sanctuary. Writing from the same publication, Harry Simons praised the single and said that it was better than Utada's previous contribution "Hikari", but stated that the "After the Battle" version should have been served as the single.

In his article for MuuMuse, Bradley Stern said that Utada's vocals and production, "brings the track to another level, transcending the patterns and limitations of most modern pop". Stern also valued the Japanese version as a "defining moment" to their artistic craft. An editor of Square Enix Music rated it nine out of ten points, commending the production and sound; they labelled it to be a "masterpiece". Blogcritics' Michael Pascua praised Utada's decision to add "Sanctuary" as the final track to This Is The One, stating, "[Sanctuary] showcases a strong musical style that isn't necessarily in the R&B flare that This is the One provides. They also help connect any video game player who hasn't necessarily listened to any of her Japanese albums or even knew that she had another English album ..." Céire Ní Dalaigh from The Arcade commented that "This track builds from the very beginning making it the perfect tune for any occasion. Whether it just be walking to work, building the pace at the gym or even just chilling out at home."

Commercial performance