TEMPLE OF HADES - DAMAGE CAP (4.2 Bi) - CANCER DEATHMASK - ARTEMIS & CLASSIC APHRODITE

If you have:
Sufficient Defense Pierce (over 1300, ideally). Equip the Cosmo mixer, Cosmo with an inscription.
The Heavens and Earth Cosmo to boost Defense Pierce.
With all these in place, you should be able to "break" the boss's defense.