The eagles patrimony is a spirit weapon that was blessed by Zeus
Reason 1
If you imbue the spirit weapon onto something it has lightning based synergies
Reason 2
The signature rites of it when translated to english from Greek:
Astropos=Lightning bolt
Astrapikis=Lightning
Reason 3
Zeus has been associated with eagles in Greek mythology
Zeus and eagle legends:
In one legend Zeus had a childhood friend named Aetos while he was hiding in Crete from his father. After Zeus becomes king Aetos is turned into an eagle by Hera out of fear that Zeus was in love with Aetos. Zeus then proceeded to make his symbol.
Also check the Wikipedia for other info i was to lazy to read or mention: Eagle of Zeus - Wikipedia.
Conclusion:
Spirit weapons need to be blessed by a god and with all these signs the Eagles Patrimony definitely came from Zeus
Random Theory I just had:
Seeing as spirit weapons have something to do with spirits it might be probable that Aetos spirit resides in the Eagles patrimony.
Many people (me included) were theorising that maybe MC is also a descendant from Zeus because they have the Eagle Patrimony, but it would be funny if it turned out MC wasnt related to him at all (only Poseidon) and MC’s ancestor found it randomly one day lmaoooo
Or its possible like… some follower of Zeus entrusted it to MC’s ancestor at some point (maybe they were getting killed off after Zeus’ fall?), but yeah, its a funny thought
sailor water lightning rn but if this can reverse imbue then it can take my third weapon since it is a shield and poof now i don’t even need access to lightning magic, should still maybe keep it though. maybe switch to a vit savant rather than weapons savant for reverse imbues