Complex sentence: Six months prior to the start of the series, a mysterious ritual held on the day of the solar eclipse to give birth to a group of magical creatures called Phantoms through humans with magical potential called "Gates", by forcibly subjecting them to immense despair.
Split into simpler sentences: Six months prior to the start of the series, a mysterious ritual held on the day of the solar eclipse took place. Its purpose was to give birth to a group of magical creatures called Phantoms through humans with magical potential called "Gates", by forcibly subjecting them to immense despair.