“Passion” is a song recorded by Japanese recording artist and songwriter Utada Hikaru for her fourth studio album Ultra Blue (2004). The song was used as the theme song for the 2005 video game Kingdom Hearts II. The song was written, composed and produced by Utada herself, while additional production was handled by Teruzane Utada and Akira Miyake. Utada had written and composed the song when she was approached to record another song for the Kingdom Hearts series, which she had contributed previously on the first video game. It also made an appearance on her 2010 greatest hits compilations: Utada Hikaru Single Collection Vol. 2 and Utada the Best.
Spoken in both English and Japanese language, the lyrical content depicts the events of past, present and future and incorporates themes of love, hope and safety. When Utada accepted the offer to record the track, she found it difficult to write a Japanese-worded version of the “Sanctuary”. “Passion” and “Sanctuary” received critical praise from contemporary music critics, who found it her most experimental track to date. Critics praised her vocal delivery and commended the production values, in contrast to her 2009 album This Is the One. Commercially, “Passion” had suffered in Japan for being Utada’s first Japanese single to miss the top spot on the Oricon chart. The song peaked at number four on the Japanese Oricon Singles, her lowest charting single and her first single to miss the top three position, but eventually tied with her 2006 single “Boku wa Kuma”.
The accompanying music video for the single “Passion” was issued for the single as well, directed by Kazuaki Kiriya. The video features scenes of anime culture that represents the image of Utada herself and features Utada in a grand hall, shot all by green screening effects and finishes with a paddock of running horses. During production, Utada had compared the video, choreography and set to 1997 animated action-fantasy film Princess Mononoke. The video was positively received by critics for its comparison sets to the video game, but received minor criticism for the lack of video game inspiration and footage.