Warning! This is important to know which the wiki doesnt tell you.
Once you interact with the blue chest it forces a name change which cannot be fixed until you've defeated the boss.
The problem is the name change applies to all instances of your saves. new or old. In addition the boss is crazy strong so if you're unable to win you'll be stuck with bad names every time you wanna start a new game!
Though if you win you get to choose the name for all 4 party members which also applies to new or old safe files. There is also a black gem you can get if you refuse to fix your name which just heals you.