User blog comment:B214/Light Novel Volume 16 spoilers/@comment-23853100-20131029020955/@comment-1359322-20131030095825

Nah he just needs the Holy Grail and Holy Cross to unseal 666. The number isn't important, he just needs the relic. Also i think the advantage of taking all 3 isn't there for Rizevim, if he takes all three, then Valerie would die and the Holy Grail might move to a new possessor. Also the power of the 3 grails are equal, Valerie's BB is a subspecies, so it's stronger than the original BB. And Rizevim just needs