Unbeatable

Unbeatable is a effect in Xenoblade Chronicles. It grants a percentage chance of surviving any killing blow with 1. The effect can occur even if the user is already at 1 HP, luck-permitting.

Overview
There isn't really any character that benefits more than others from being able to just ignore dying. It could be argued that a tank is likely to quickly take again and so bait the healer into wasting something on them, but this is not necessarily a tank-exclusive problem, as non-tanks are unlikely to lose the  exactly when the gem triggers.

Certain plot-restricted weapons have a special variant of Unbeatable that has a 100% rate of triggering, making it impossible for the character to die.