[@Atroposer] Just an FYI. My take on Hades is going to be that due to Persephone he has long neglected his duties. Coupled with the fact that their power has lessened that would be the reason for so many souls escaping or being taken from Hades. 

I was thinking that someone unnamed could have placed a charm on Hades to focus him on Persephone as that extra reason for why he neglected duties whilst Persephone would have been with Demeter. Which would also be his reason for awakening as I'm also thinking that someone could have stolen Persephone away and in Hades' rage the charm was broken and he has realised how unruly the underworld has become, so he would be rather angry to start with I'd guess and very driven to get things back on track whilst he looks for Persephone. 

I don't want to theorize who could've cast the charm or who could've stolen Persephone just yet but I thought they would perfectly set him up in the RP. Maybe they could come to fruition in book 2 or 3? if we get that far.