Gentle Rain is a song in Mother 3 that plays when Flint brings Fuel back to his injured father. Shortly after they reunite, it begins to rain, giving the song its name.
This is also the first entrance of a reccuring musical motif throughout the game; the melody here also plays during "Sorrowful Tazmily" and "Mind of a Thief", as well as briefly during other tracks.
Origin/Reference:
It is all too likely and could even be said to be obvious that the main melody of this song and its motifs is based on "preso" by José José in the violin melody part and the part where it says "Preso de la cárcel de tus besos de tu forma de hacer eso a lo que llamas amor, preso abrazando tus caderas condenado a lo que quieras"