Advice for responding to "Kwabang" attack when playing Japan?
The problem with the Kwabang attack is it can give the UK a decent foothold in Asia, as well as denying Japan some early IPC, and it really screws with Japan's starting strategies.  

Part of me wants to say, "Just ignore Kwangtung, go after Hawaii, and start grinding out transports and armor turn 2 for a mainland attack", but I think the Kwangtung attack swings things enough that you need to deal with it first turn.

While 5 infantry plus 2 battleships against 1 infantry anywhere would normally be overkill, in this case I don't think it is, because:  what else are you going to do with them?  

To successfully attack the Pearl Harbor fleet, I feel you should throw everything in your fleet and air force at it, and if you're already sending your bombers into China instead of Hawaii, and you probably want at least one battleship in Kwangtung for the bombardment, there's not much left you can send against the Pearl Harbor fleet.

Sooo... finally to your question, where does that leave us?  I guess it depends on what the US does.  With an intact fleet, I think the US have two options -- harass Japan so they can't start a mainland invasion, or swing through the Panama Canal and support UK's landfall into Germany.

If the US goes after Germany -- good news, it's not your problem, at least not directly.  You'll just have to push hard into the mainland to advance into Russia, and find other ways to support Germany (ideally by eliminating the US and UK presence, setting up a mainland factory, and cranking out infantry and armor from the east coast of China).

If the US uses their first turn to move towards you, their fleet can't make it to Japan in one turn, so you'll have a turn to buy units and bulk up.  If you're playing with two-hit battleships, consider one; otherwise, consider subs and destroyers to counter their navy.  You'll want to go after the US navy pretty fast, because they'll do one of two things:  camp out in the Japan sea space, or start island-hopping with the UK to drain you of IPCs quickly.

Oh yeah, as for Manchuria, if you think you can get away with it, leave one unit in Manchuria for the defense.  

Wow, that ended up being longer than I intended.