This was caused during the moment when Devon was absorbing Zaylee's blood, if Devon hadn't stopped had continued to absorb her blood and life essence, then it could be said that he would have broken one of the chains which were wrapped around his body.
It might seem as though the loss of one chain out of nine didn't mean anything, but to Devon, it was a very huge matter. Not only would he acquire more power, but he would also be able so to access more memories that had flooded his head during his devil transformation.
During those short moments at which his hand was holding on to Zaylee's neck, Devon's head was being bombarded with ancient memories which he didn't even know about. The memories contained everything he needed to know about the devils.
Their skills, innate abilities, weapons, oddities, and everything. It was like he had all the devil's inheritance right in his head, and this was precisely the reason he needed more time to achieve his devil form.
