The second movement of this sonata is similar to the first, albeit more subtly, in having a simple-sounding opening only to increase in rhythmic energy as it goes along; this process is repeated twice due to the standard exposition repeat (2:21).
That aside, we find ourselves with what may seem to be a typically gentle slow movement from Mozart... up until the halfway point is reached. In the development section (4:42), Mozart engages into a realm of seriousness that's entirely unique in the whole sonata, filled with minor-key harmonies and even a few dissonant passages to boot.
Once the recapitulation is reached (6:02), the section where we would expect a return to the exposition's material and general mood, everything is now cast in noticeably darker colors. In effect, the somberness from the development has changed the outlook on the music we had heard before, and the struggle to cast that aside persists until the wistful final bars.

Piano Sonata No. 15 in F major, K. 533
II. Andante

Composer: Wolfgang Amadeus Mozart

Soundfont: Final Fantasy X

Movement 1:    • Mozart - Piano Sonata No. 15 in F maj...  

Movement 3:    • Mozart - Piano Sonata No. 15 in F maj...  

Super Mario 64 version:    • Mozart - Piano Sonata No. 15 in F maj...