I’ve come to a bit of realization. Well, more of a theory. Maybe it was only when [Light] Demon Lord Marbas, the one that supposedly helped Belial, died that Marcho became one of the big three. If so, then it really is reasonable to assume that she was the weakest among the current big three. What I’m saying is, it makes sense that she was the one that Black targeted back in volume 5.
Anyway, I hope you enjoy the new chapter!