Goddess sisters of DXD

In the world where exist supernatural,devils,angels,fallen angels ,yokai,dragons and dragon gods exist also 2 sisters goddess. Everyone think that ophis and great red are strongest in universe, but not very many people know about 2 goddes who each one is strong enought erase all fractions from existence without breaking sweat. They are know how Leona, the true goddes of sun and Diana, the true goddes of moon. Together are strong enough destroy multiverse.What happened when two sisters decide go to human world and meet devil group with perverted dragon?