Based on other games with insane bonus bosses (like Alphadia, Eclipse of Illusion, Eve of the Genesis, and not to forget Maidame Curie in Asdivine Dios and Menace) the only thing I can think of at this point is to grind to a ridiculously high level, and hope that it works.

Hopefully it won't be a complete waste of time (meanwhile I am enjoying watching high-level bosses do 100-200,000 damage to Julie and Fleon, and both of them staying at 1HP. I'm definitely getting my money's worth in the entertainment department) :woohoo: