Blood of the Guardian of the Altar
Blood of Embryo's high-level apostles Isadora and Maliss who protect the Altar inside the Seal of Shillien. Take it to the Lord of the Dusk Baro Negrado.
Not dropped by monsters.
Cannot be spoiled.
The chances are official (x1). On servers with x10, x100 and higher rates, drop and spoil come more often.