So after about a year of giving up on the Tank boss. I felt in the mood to play again. 
I think I've figured out how to get him this time, though I died again and pressed the Guide button, promptly followed by Y. But I plan to at least finish him off.
On further thought though... I don't know if I'll ever finish this game. I rarely finish JRPG's as is. So did you finish it?