Sentinel (Defender in the Japanese version) retains its task of reducing incoming damage. Serah Farron and Noel Kreiss start with Sentinel, but the only latter specializes in the role. The role loses Evade, Counter, and Elude, but gains Element Guard. There are also numerous Paradigm Pack monsters that serve as Sentinels. Lightning in the Lightning's Story: Requiem of the Goddess DLC scenario has a role based on the Sentinel called Knight.
Sentinel was available as a secondary Discipline of War in the first iteration, but since version 1.20 it was removed.