Passion (Hikaru Utada song)

"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.