Complex sentence: He soon discovers that his new title is quite literal, as a nefarious spirit named Yasunori Kato, originally a human who became a demon from the strength of his hatred for humans and desire for revenge against their actions on the Youkai.
Split into simpler sentences: He soon discovers that his new title is quite literal, as a nefarious spirit named Yasunori Kato appears. Originally a human who became a demon from the strength of his hatred for humans, Kato desires vengence against their actions on the Youkai.