It's the game lore behind it. Chuuga and Buyaka are siblings, one is a "good" demon for some reason and the other one is a "bad" demon according to the game lore. It's a small flavor to the game that many people miss.
Game mechanicswise it's pretty much the game's way of saying "you can't have best of both worlds, either protect yourself or have this effect"
Sauce:
http://warofdragons.com/artifact_info.php?artikul_id=2854
It's a small, old easter egg and not gonna lie, I wish the parent company kept the old devs who put these stuff in the game.