Re: (Nutaku) Hellfire Girls
I managed to play an event on the Japanese version, if anyone has any questions. Their version looks newer, so I'm not sure how accurate it is to go off that version.
The event only consumes Energy. (you indirectly need ATK to build your strong decks for the battles)
You can get free Event box rolls. It was a little unclear, but it seemed like there were daily reward tickets and random reward tickets when winning an event battle. I got 3 or 4 with about 100 energy.
There was a normal mode, which I could do some of while under level 10.
There was a hard mode with an event boss that had 1.5 million HP. A little unclear on the battles, but if you spend extra energy you can do quite a bit more damage than normal. You could also attack more than once.