Rex spreads his eyes open when he realized that as it turns out, a third party was involved.
During his time when he was still inside the human territory, Rex came across an entity called the Witch of Chaos that was said to be able to help him get rid of the Eternal Curse that bound him with Caldiora for good.
It was Jarvald that introduces him to this Witch of Chaos, and she wanted Rurvi in exchange.
Jarvald briefly mentioned to him that the Witch of Chaos is a title that dated back to ancient times when the ancient humans are still at their very peak, the Witch of Chaos is an anomaly and was said to be given power through something called The Cursed Grimoire of Mary.
The Witch of Chaos evokes cursed phenomena and is thus banished from every human estate.
