"Hikari" is the original, Japanese version of "Simple and Clean"; it was originally released on Utada's Deep River album. It was used in the Japanese versions of Kingdom Hearts, Kingdom Hearts Chain of Memories, Kingdom Hearts Birth by Sleep, and Kingdom Hearts Re:coded. The name Hikari (光) literally means "Light" in Japanese, a universal force in the Kingdom Hearts universe.
"Simple And Clean -PLANITb Remix-" and "Hikari -PLANITb Remix-" are versions of "Simple and Clean" and "Hikari" remixed by Russell McNamara at PLANITb Studios London, England. The PLANITb Remix is faster, longer, and has more of a dance mix feel to it than Utada's original song. A shortened version of the remix is heard during the opening movie of Kingdom Hearts, Kingdom Hearts Final Mix, Kingdom Hearts Re:Chain of Memories, Kingdom Hearts Birth by Sleep, Kingdom Hearts Birth by Sleep Final Mix, and Kingdom Hearts Re:coded.
"Hikari -KINGDOM Orchestra Instrumental Version-" is an orchestral version of "Hikari", and can be heard in Kingdom Hearts and Kingdom Hearts Final Mix in the opening menu cinematic which appears if the player lets the opening menu sit for about fifteen seconds. The orchestrated version is also featured when Sora reads Kairi's letter in Kingdom Hearts II and at the end of each scenario of Kingdom Hearts Birth by Sleep. The orchestrated version is used during the opening movie of Kingdom Hearts 3D: Dream Drop Distance.
Another, softer arrangement of "Hikari" play in Kingdom Hearts when Sora stabs himself with the Keyblade of heart.
"Simple And Clean -Ray Of Hope MIX-" and "Hikari -Ray Of Hope MIX-" are versions of "Simple and Clean" and "Hikari" remixed by PUNPEE that were used during the opening movie of Kingdom Hearts HD 2.8 Final Chapter Prologue. This version is shorter in length in comparison to the original and the PLANITb Remix. The Ray Of Hope MIX has a similar dance mix feel like the PLANITb Remix, although a few clicks slower.