Complex sentence: Hannah Snow-Hannah is the protagonist of "Soulmate" and an old soul who has been reincarnated since the Stone Age when she first saw her soulmate Thierry, who was known as Theorn at that time while she was known as Hana of the Three Rivers.
Split into simpler sentences: Hannah Snow-Hannah is the protagonist of "Soulmate" and an Old Soul who has been reincarnated since the Stone Age when she first saw her soulmate Thierry. Thierry was known as Theorn at that time, while she was known as Hana of the Three Rivers.