Theory about a B major on a C minor song

[strav101]

but my instinct is, there wasn't this kind of thought applied in the making of, it just sounded good to somebody and got the effect they desired.

I agree. The chord was probably found only fiddling round on a piano - no theory, just using the ear

[jsaras]

For starters, trying to think in terms of key centers is a lost battle. In my mind, every root is its own tonic. That said, the B major could be thought of as a leading tone chord that leads to C minor (and/or vice-versa).

[KLS]

Also, please remember that a lot of pop songs can only be partially analyzed according to the rules of classical tonal harmony. There are some chords in pop songs that aren't supposed to fit with the rest of the harmony. We might call these "surprise" chords. They are there to keep the song interesting and to provide harmonic contrast with the rest of the progression. They are placed in strategic positions in a song and they call attention to themselves by sounding different from the harmony surrounding them. Since this chord ends the chorus, it is calling attention to what is happening there. Something the songwriter wants you to remember - probably something in the lyric.

I like the idea of it having a leading-tone effect back to the C minor. Or it could be heard as a type of "secondary dominant" that never resolves anywhere. Again, it's purpose seems to be coloristic and not functional.