User blog comment:Metadwarfosis/Slane Theocracy- Massive war or Surgical removal of Black Scripture?/@comment-26815449-20151228022640/@comment-27168967-20151229111151

It's probably the de facto storage vault for Black Scripture equipments, World Item and some other Yggdrasil expendable items. I can't imagine the Black Scripture members would store their equipments somewhere where the highest security is not in place. Since it is also the one place that stores the one set that's specifically for Zesshi, I would guess it's also the one place where Zesshi lives in solitary most of the time.