Complex sentence: Yoko had conceived the relationship between Caim and Angelus as a parasitic one, with Caim as the host, but Iwasaki wanted to create a different type of romance and instead wrote their relationship as a love story.
Split into simpler sentences: Yoko had conceived the relationship between Caim and Angelus as a parasitic one, with Caim as the host. Iwasaki, however, wanted to create a different type of romance and wrote their relationship as a love story.