The energy consumed all comes from the blood and flesh power of Fishman Island.
The fish-men could even sacrifice all their blood and flesh, unleashing their strongest attack, fully manifesting their king, the Great Fool.
A thousand spirit stones are worth it mainly because Small Knife feels he can learn something from it.
Because it seems the warriors master the blood and qi power much better than these fish-men, this special construction seems more suited for him.
It's clearly not very fitting for the cold-blooded fish-men, although outside it's a common ability, but it's very useful to him now, and there's no copyright, once he comprehends it, it becomes his own.
So, Small Knife took out a thousand spirit stones and painfully made the trade.
He saw the spirit stones swiftly absorbed by the Earth God, turning into dust.
The blueprint transformed into runes and merged into his mind.
