Originally Posted by
Cleretic
I mean, we've seen the forge Eureka. It's a primal, and it looks like basically a really fancy cube. You only see it at the end of Hydatos, so fair enough that a lot of people haven't. There's no confirmed evidence that the primal Eureka and the Allagan Eureka were connected--the primal Eureka likely was given that name by the Sharlayans based on the same myth that led to the island getting the name, although we don't know that for sure--but the primal Eureka does go back to at least Allag, as that's where the first known Eurekan weapon-primal, Odin, was first recorded. So it's entirely plausible that they're connected, but it's not confirmed.
While we know very little of the primal Eureka's history beyond that, it can be surmised that sometime after Allag Mhach came across either it or its creations. On top of Proto-Ozma, the first bosses had abilities that looked awfully similar to some of Scathach's and Diabolos'.