"Dearly Beloved" is the opening theme to all Kingdom Hearts series games and is composed by Yoko Shimomura. "Dearly Beloved" is considered the main theme of the Kingdom Hearts series.
It begins playing as soon as the game loads and plays over the opening Menu Screen in a loop. However, if you continue to listen to "Dearly Beloved" without pressing any of the buttons on your controller for approximately 10-15 seconds, the screen will open up to Opening Menu Cinematic or Demo Loop, which will play the orchestrated version of the Kingdom Hearts theme song. There is also a Reprise version that plays after the credits at the last screen in Kingdom Hearts and while viewing your Battle Report results in Kingdom Hearts II.
The original version of "Dearly Beloved" was composed solely on the piano.
The reprise of the original still contains the original melody, but this time combines piano and mallets.
The Kingdom Hearts: Chain of Memories version contains the orginal melody played on the piano, along with a secondary melody played in the background by a synthesised instrument.
The Kingdom Hearts II version transformed "Dearly Beloved" into a full orchestral piece (although the piano remains dominant), containing only the secondary melody.
The reprise of the Kingdom Hearts II version contains the secondary melody, but played only on the piano.
Kingdom Hearts 358/2 Days contains a nearly identical version of the Kingdom Hearts II "Dearly Beloved" reprise, only this time it has the flute used in Roxas' Theme.
Kingdom Hearts Re:coded contains a new version of "Dearly Beloved", with a slightly faster tempo.
Two arrangements of the song, entitled "Dearly Beloved" and "Concert Paraphrase on Dearly Beloved", appear in the Piano Collections Kingdom Hearts.
Kingdom Hearts 3D: Dream Drop Distance's version of "Dearly Beloved" retains the original theme with pianos, violins, xylophone and plucked violins, then the melody is played with flute and then has a slightly quicker part where a tambourine comes into play.
The themes "Friends in My Heart", "Always on My Mind", "March Caprice for Piano and Orchestra", and "Fantasia alla Marcia for Piano, Chorus, and Orchestra" are variations of "Dearly Beloved" that can be heard in Kingdom Hearts. "Musique pour la tristesse de Xion" from the Piano Collections Kingdom Hearts Field & Battle album, contains melodies from "Dearly Beloved". "Dearly Dreams", the field music for the Mirage Arena in Kingdom Hearts Birth by Sleep, also contains some melodies from "Dearly Beloved", as does "The Key", the battle theme to Ventus-Vanitas.
