I'm also muddling my way through the game and just now after a few weeks found what appears to be a calibration for the timing of the button presses i think. I goofed with it and it seemed to help me out when I tried to play a hard level song (actually passed it with no fail!) Immediately afterward so I think it might help some of you struggling. Most other games of this type will have a calibration setting to offset your personal handicap and align it better.
On the last tab at the bottom all the way at the right is the options tab. Touch that and then just above the "FAQ" button there is a wrench with a cog icon. Scroll all the way down to the bottom after touching the icon and you will see a gauge that looks like "50--------50", hit the purple button below that. The game will play a short melody, and you should touch the bubble when you hear the "beat" coinciding. The game will then adjust to your timing and then play the song again this time with the familar silver circles coming down and you should hit the bubble at the beat. After it is done it will then keep the setting for you so you can go back and adjust it as you get more comfortable. Mine was like -11 or so. So far it seems to have helped my game. You can all laugh at me if I don't know what i'm talking about since I can't read japanese but try it.