On the physical level, Nesanel is indeed unkillable, but this injury reflected in his Alchemy Matrix, producing a fatal Soul Scar, much like a complex machine developing numerous cracks within. The machinery can still operate, but if it overloads, no one can guarantee whether these cracks will widen, parts will break, and the machine will collapse.
Nesanel tentatively clenched his fist, with the soul and flesh reflecting each other, he could feel a faint pain in his flesh, preventing him from fully tightening his fingers.
He cautiously summoned Ether. A small amount of Ether flowing wouldn't cause anomalies, but once the scale of Ether's invocation grew larger, the Alchemy Matrix showed signs of tending towards losing control.
"Damn it, they still achieved their goal," Nesanel muttered under his breath.
"What goal?"
