Importance of Strain:
The Orcs perform a magic ritual in which they they infuse the blood of more powerful beings into their own bodies to enhance their strength.
However, once two different types of blood are mixed, the organism that receives the mixture is fundamentally changed.
For instance, Humans created by Gran Kain are structurally different from all four other races.
There have been some cases where the change was reversed by using Stun magic and a skill to remove the mixed blood from their veins.