The curse affinity.
"They have no knowledge of you ever having it."
It was his only ability that was never directly given by Skill Weaver.
"Hence, they could never see it in the tome."
Then that could only mean…
"....You were the one who gave me the curse affinity."
"Correct."
"...."
It was the only elemental ability that he could continuously progress.
After all….
"That is my power, and that is the power that's inside that body of yours."
"...."
"The more you use the abilities that Skill Weaver has given you, the more you're allowing Jin to fully assimilate with your body."
"Then why haven't you warned me?"
"I couldn't. The only thing I could do was give you the curse affinity. It was my way of protecting you from its influence."
Snap!
The other Brandon snapped his fingers once again.
"You've been relying on it more often, right?"
"Yeah."