Complex sentence: Hawaiian folklorist Glen Grant was known for his "Obake Files", a series of reports he developed about supernatural incidents in Hawaii; the grand bulk of these incidents and reports were of Japanese origin or concerned obake.
Split into simpler sentences: Hawaiian folklorist Glen Grant was known for his "Obake Files", a series of reports he developed about supernatural incidents in Hawaii. The grand bulk of these incidents and reports were of Japanese origin or concerned obake.