No, I think it is the difficulty of the boss that determines the music.
Boss theme 1 = hard
Boss theme 2 = harder
Boss theme 3 = harderer
But it’s just my theory.
When encountering a traveler's hub quest boss, "battle intro: i'm gonna win" is used but "boss battle I" is always used when fighting the boss
I know lol
Wait, this complicates things!
I makes your third, sixth, and ninth party members the most important members of your party.
But they could've at least used "Boss Battle II" to match the theme of major NPCs. It kinda makes me feel like 1st, 3rd, 4th, 6th, 7th, and 9th party members don't really matter.
Eh.... it'd be pretty boring seeing the same theme being played for like 7 bosses in a row
It would be cool if the party member bosses had a battle theme that was just for them.
What do you think?