Complex sentence: In the moment he regained his memories of the previous life Natsume was killed, he performed the Taizan Fukun Ritual and revived her but then he leaves Natsume.
Split into simpler sentences: In the moment he regained his memories of the previous life, Natsume was killed. He performed the Taizan Fukun Ritual and revived her but then he leaves Natsume.