Chorina:
The Sea of Spores used to have a barrier, but it couldn't stop the sea expanding as the Energy of the Sea of Spores got stronger.
So the Ivory Tower found a way of creating a new barrier: "Killing poison with poison"...
We're using the very same Energy of The Sea of Spores which made the Sea of Spores more dangerous as our source of energy. But there's a problem. This energy is very unstable and keeps trying to spread and escape.
So I had to come here for the maintenance of the barrier. I'm capable of the most minute distribution of energy for maintaining the barrier. As long as I'm here, you don't have to worry about Sea of Spores.