the.com/invulnerable
Immune to harm, until the plot requires a single conveniently placed weakness.
means Incapable of being wounded, damaged, or successfully attacked by any conventional means.
from From Latin invulnerabilis: in- (not) plus vulnerare (to wound), from vulnus, wound — literally unwoundable.
Achilles clauseMyth insists invulnerability always leaves one fatal spot
Comic stapleSuperman is invulnerable except to a green rock
Word relativesShares its root with vulnerable, its mirror twin