See Final Fantasy X.
When attribute is added to defensive equipment, if that character is attacked, they automatically use potion/hi-potion/X-potion/Mega potion depending on what is more available and comes first in the items list, without taking a turn.
--Boss: Seymour Flux--
*During battle after all die except Auron*
RL Person A: WTF? Seymour poked Auron with his lance!! Now he's a zombie!
RL Person B: Hey, he's using auto-potion!
RL Person A: WTF?!?! NO!!! He's gonna die!!! WTF IS WRONG WITH YOU AURON? YOU DON'T HEAL A ZOMBIE!!
RL Person B: Well he just killed himself now...
RL Person A: WTF? I almost won too!!
Machina A v/s Auron
Machina A attacks -- Auron -865HP
Auron Auto-potion +1000HP
RL Person A: Hey, fricken sweet! Not that it matters... He has fricken 5,000 HP.