It took me one try actually.
In fact, the only boss that gave me any trouble was.... ummm.......
The Havoc Skytanker at the end of Chapter 6 (I think) when they're at Palumpolom or whatever it's called. It killed me twice before I discovered you had to kill the OTHER parts first.
Kimi wa ne tashika ni ano toki watashi no soba ni ita
Itsudatte itsudatte itsudatte
Sugu yoko de waratteita
Nakushitemo torimodosu kimi wo
I will never leave you