Shield Bullet

Shield Bullet is one of 's support Battle Arts in Xenoblade Chronicles. It applies a "shield" to the target that blocks an amount of damage for a time.

Overview
Shield Bullet is best thought of as providing "overheal": temporary HP that sits on top of actual HP and must be depleted before any actual HP can be lost. This essentially makes it a way to heal people that are already at full health, with the caveat that it goes away after a time. Because of the timer, the effect is wasted if no damage is taken, and gains full value if the entire thing is damaged - therefore, it is best applied when it is anticipated to be fully used, rather than just throwing it on someone as insurance from being randomly whacked. (That said, the timer is reasonably long.) Its main downfall is its long cooldown and expensive AP requirements.

Overheal does not factor into how much HP a character has, so it can save them from instant death effects (as they deal damage equal to current HP). Overheal takes precedence over health no matter what the source of the damage is, be it a direct attack (of any type), a debuff, a spike, or even self-damage.