Hikaru Utada's compositions for the Kingdom Hearts games are just one of the many reasons these titles became a runaway success story for Square-Enix. Featured here is Sanctuary, the English-language version of her theme to Kingdom Hearts 2. (The Japanese version, entitled Passion, is available here.)
Hikaru is massively popular in Japan and her album First Love became the highest selling album in Japanese history. In the West, she's signed under the DefJam record label, which leads me to wishful thinking about her contributing to forthcoming expansions of the DefJam fighting game franchise.
UPDATE: By the way, how awesome is this Hikaru Utada cover of Boulevard of Broken Dreams?