understanding popular harmonic prog.

[Farnaby]

As I suspected, the examples quoted are basically songs with only one or two chords throughout, so these don't really count as they have such limited tonality of any kind.
There are songs however which postpone the tonic chord until well into the piece - the song Sweet Georgia Brown is a good example, Moonglow is another.
By definition really a piece of music must contain its tonic if it can be defined as being in that key. I would be surprised if there are any real exceptions to that.

[Farnaby]

There's a chord progression which is a apparently extremely popular in Japanese music: IV V iii vi. In C major that would be F G Em Am. Of course it's also possible to hear the 6 as the tonic.

What makes you think that is in C major?

[NAD]

There's a chord progression which is a apparently extremely popular in Japanese music: IV V iii vi. In C major that would be F G Em Am. Of course it's also possible to hear the 6 as the tonic.

What makes you think that is in C major?

To be clear I use C major and A minor interchangeably although arguably you'd use an E or E7 rather than Em if you're thinking of A minor harmonic. Other than that I really don't see any other way you could possibly interpret F G Em Am. I guess just try jamming over it and see what you end up playing. I'd be willing to bet you'll gravitate to C major or A minor unless you're into some freaky avant-garde stuff.

[jancivil]

There are songs however which postpone the tonic chord until well into the piece

Well, I heard the beginning bit, and while there’s a real obvious I, he isn’t going to it but preferring to hang out at IV. So per the OP there’s the possibility of IV of IV (bVII) that isn’t a native property of major key.

[cmaxx]

If you're still referring to Fireflies, he goes to the I chord (Eb) in the 2nd measure-
V-I-IV-IV...no secondary dominant or bVII mixolydian here...

[jancivil]

duplicate

[jancivil]

per the bVII remark, it regarded a specific question in the initial post, how is there A in the key of B.

you are correct, I missed the I before IV.

[jancivil]

another duplication

[jancivil]

There's a chord progression which is a apparently extremely popular in Japanese music: IV V iii vi. In C major that would be F G Em Am. Of course it's also possible to hear the 6 as the tonic.

What makes you think that is in C major?

To be clear I use C major and A minor interchangeably although arguably you'd use an E or E7 rather than Em if you're thinking of A minor harmonic. Other than that I really don't see any other way you could possibly interpret F G Em Am. I guess just try jamming over it and see what you end up playing. I'd be willing to bet you'll gravitate to C major or A minor unless you're into some freaky avant-garde stuff.

Key of A minor is not interchangeable with key of C major in itself. In fact, C major has a C tonic and A minor has an A tonic. There may be contexts where ambiguity of the two is perceived or even is sought but your conflating two things as one per se isn’t necessarily anyone else’s problem and is obviously a dodgy basis.