You are a typical arrogant (in terms of English-using) person who feels that English absolutely must be used in every country practically 100% of the time in a job that seems to be international in nature (like IT work). Welcome to Japan! It's not that way.
You complained that for certain global companies you "scarcely imagine how they'd communicate with the head corporate office otherwise". The head execs might, but even they will have problems with English. Trust me. I've been researching that a lot recently. As for little old you, well, Mr. Programmer, you are very unlikely to be contacting Mr. Big back in the U.S. for your job. You will spend far more of your time communicating with coworkers, your boss, and other departments, and unless you get a foreign company branch to hire you here, expect most of the time it will be in Japanese.
So, you should have done your homework before coming, so you can locate and focus on only the foreign branch offices (or the rare Japanese company like Uniqlo or Rakuten) that will have more (but not necessarily 100%) of its office language as English. It's not fool's gold here, but it will take a bit of prospecting!
Once you find one, then the next hurdle rises in front of you...will you meet their requirements?
P.S. in my research, I've found that among engineering types, software engineers speak the least English.