Sagara is a multi-dimensional eldritch horror that exists to give power to species and help them evolve. He's a force of nature, you can't "resolve" or stop those. You'd have an easier time removing the evil from the heart of man.
But that's a rule of the universe and the whole point of Kouta's resolve was he wanted to break those rules. Wouldn't it have been more satisfying and ironic if he had found a way to break Sagara's rules as well?