User blog comment:Piyush Banerjee/Shin DxD 2 discussion/@comment-37165251-20181202115344/@comment-1605975-20181203225757

@Merkarion Zaoroma could cooperate with Hades to free Euclid in order to have him unseal the Malebranche, assuming that my earlier theory actually ends up coming true. I'm not too keen on Euclid coming back either, but it might be a good chance to take him out once and for all. Simply imprisoning your enemies is just begging for them to come and cause trouble later.

As for the Malebranche, there might be restrictions in their use just like how the King Piece cannot be used by individuals who are already too powerful. Perhaps something like only descendants of the Old Maou with a certain amount of power and talent can fully synchronize with them without drawbacks, while other powerful beings run the risk of overloading themselves from the immense power of the Malebranche and destroying themselves. As such, it would be deemed too risky for Balberith and Verrine to use them. As such, the Malebranche could fight by themselves or given to Devils with lower power, giving the DxD team a fightning chance against them. We'll see what Ishibumi has planned for that in the future.