The patern im starting to see is that ALMOST everyone is replaceable for the Goddess, but it seems ONLY Mars and Erin are constants she doesnt seem to want to erase, If you let Erin kill himself in the bad end she punish you and the world for all eternity, as another way of entertainment of course, even tho she can just replace another hero, she has an special kink of seeing Erin suffer and i think she knows someone like Mars is quite unique in many aspects, meaning she knows she cannot just dispose of him, and the Aith thing is either that, or she just was made insane by the Goddess for the lolz, and Mars doing that to Aith honestly is better than her and Cecille having to fight and eventually forcing Erin's hand into doing something extremelly regretable, after all we know how manipulative and venomous Cecille is, she would find a way to make Erin kill her or even kill her herself in some way, i wouldn't find that impossible.