Trails in the Sky games, three arts (spells) called Earth Guard, Earth Wall and Gaia Shield. They give physical immunity against one attack to the targeted party members (Guard is single-target, Wall is an area, Gaia Shield is the entire battlefield).

99% of enemy attacks in Trails in the Sky are physical and the spells are cheap and fast to cast, they make the game easy on lower difficulties and the highest difficulty practically demands you use them.

They were also never in Trails again after Sky the 3rd