Character shields (also known as plot armor or plot shield) are plot devices in films and television shows that prevent important characters from dying or being seriously injured at dramatically inconvenient moments. It often denotes a situation in which it strains credibility to believe that the character would survive.
"The art is nice, but the concept is obviously pretty stupid. Hell, just the fact that they're using the most broken character with plot armor as thick as fangirls' raging hardons for him, from Naruto, against someone who was shown to only be a mediocre bender at the beginning of the series (the form of Zuko used here) should tell you something."
--Anonymous, from 4chan's /co/ board, describing a Deviantart comic depicting Naruto's Sasuke fighting Avatar's Zuko.