Is there a way to get the demonic seed after the Erosian War? Wendis says the seeds we planted in the mine have borne fruit, but for the life of me, I can't figure out which mine or seed.
I assume you're referring to Wendis's line "Do you remember those seeds we planted in the mine? They should have born fruit!" However that's not about literal fruit. It's metaphorically referring to the process we set up to mine for True Stone, or True Gold if we already had True Stone.
There is a Demonic Fruit you can get from the dark elf mage wandering Yhilin's slum in Chapter 5, but currently there is no way to get Demonic Seed except from the Great Thenoursan War. I believe there is supposed to be an alternate way eventually.
Nope, Either you use the seed on Sabitha or don't undermine her during the thenoursian war.
Pretty easy don't kill the blue demons and don't use the seed, that's the optimal outcome.
Or if you do kill the blue demons (why they're harmless) use the seed on sabitha.
The real bit you can easily miss is the crystal of harmony, even if you get a good result during gawnfall the cult goes into seclusion after the war and you miss out.
Thanks! I got the fruit, and have the rest done. But I'm saving another optimized run until after the game finishes.