Complex sentence: She is soon joined by Yū Isami, an ex-Reclaimer who leaves Orphan after learning of the catastrophe it seeks to unleash, and the both of them enter upon an adventure, which may decide the future of humanity.
Split into simpler sentences: She is soon joined by Yū Isami, an ex-Reclaimer who leaves Orphan after learning of the catastrophe it seeks to unleash. The two of them enter upon an adventure which may decide the future of humanity.