You mentioned that in your trip to Japan, the best part of the day was being able to sing as loudly as you wanted, with no one around to hear. I sing because it gives me pleasure to hear it when it's right. I always bring a kind of shyness to the experience when I sing in front of people, because I'm more comfortable as a singer producing a sound that my own ears enjoy. If others want to listen to it, they may, but I'm not altering my posture toward them. That to me is a more comfortable thing than stage work.
Privacy goes with singing.
There is no ulterior motive other than than an idea wants to get expressed. So the initial impulse has taken care of itself. You realize you're writing to someone, even if it's to a soulmate you're hoping to find. In childhood, the music was born out of the fact that I can sing. With writing, I just had to write these things.