Complex sentence: This was the result of his birth father daimyo Daigo Kagemitsu forging a pact with 48 sealed demons to rule the world in return that each demon could obtain a piece of his unborn child's body.
Split into simpler sentences: This was the result of his birth father daimyo Daigo Kagemitsu forging a pact with 48 sealed demons so that he might rule the world. In return, he promised the demons could each obtain a piece of his unborn child's body.