A crystalline mineral with a faint glow that shifts color by energy state. A fistful powers a city block for a year. It runs Britannia's fleets, computes like a living circuit, carries unbreakable communications, and — in sealed laboratories — has begun doing things to time itself.
To Frysians, Etherium is sacred: the world's stored memory, not the world's battery. To Britannia, it's the foundation of a divine mandate. That single disagreement, more than any border or treaty, is why the north is occupied.
Two facts the Empire does not advertise. First: their richest source isn't a mine, and mined is not the right word for how they get it. Second: the more Etherium you concentrate in one place, the stranger that place gets at night.