Although he claimed to be different from the Nest Will's intentions, Ian had indeed been significantly eroded by the other's Spirit Energy.
The only thing that took the Nest by surprise was one detail—it had merged the memories of The Great Elder and all those it had devoured in the past, and together they didn't go mad like Ian did on his own.
The monster held a sword and appeared rational, objective, and calmly detached, yet it felt a sense of dread towards Ian.
Because Ian's madness was near to achieving something 'impossible'.
Through the recent psychic contact, it understood that Ian hadn't lied and also grasped Ian's speculations about the Star Prison Tianyu... to the point of feeling despair.
But Ian had already emerged from despair, still firmly clinging to his dream.
It wasn't that Ian couldn't resonate with the Nest Will due to being different; it was that the Nest Will found it couldn't keep up with Ian and thus couldn't resonate with him.
