[quote=@Unoedipal] "The 726th Holy Grail" refers to the fact that 725 times in the past, "something" that we call a Holy Grail's materialized. They're not the same device or something, this thing was 100% engineered by the Three Great Families (with tweaks by the Zetsumei). The Grail has seven Master slots. When they're filled, they're filled. If you get enough prana and have the right system, it's theoretically possible to summon a Heroic Spirit without the Grail, but they won't be accounted for by the Grail System since they weren't summoned by the Grail. You can't just brute-force the Grail into opening another slot, especially if you're just a group of randoms who aren't even related to the Three Families. Not even Zouken could do that. If you give a good enough justification for why this random cult's managed to develop a ritual that makes something similar to a Servant, then sure, knock yourself out. That said, it won't be related to the Grail and when it dies its juice won't go to the Grail; it'll just be there. [/quote] I think the ritual for summoning a standard servant is already something that was understood by humans, so with enough time and experimentation you can replicate the process, even if summoning the eighth servant does require an atrocity (not that Nasuverse is averse to those). Even if the servant's own dead body doesn't power the grail, this does mean that the cult in question now has a way to reach the Root without sacrificing their own servant, which means you keep your super strong magical friend a bit longer AND you don't need to sacrifice him to get the super secret bonus, which would keep said Servant from turning should it ever find out.