So, every few hundreds of years, there will be this "carrier" and its "protector" born right? So what's the carrier's purpose for being born? I thought with that ability, the whole purpose of the carrier is obviously wreck havoc on the world.

But then again, the protector's job is to prevent the carrier in destroying the world or something without actually killing the carrier? Why? Why release the carrier in the first place?

Like creating a nuclear time bomb, THEN creating a protector to protect the nuclear bomb from being used by all bad guys. Either not releasing the bomb in the first place, or diffuse the bomb immediately.

So a kid with terrible devastating ability is born, and a protector to protect this kid of being used by bad guys. Why having a kid with that horrible ability in the first place? I can't think of a scenario where controlling millions of rats could be used in a good, healthy, and productive manner to society, other than redirecting all those rats to a burning fire.