When you take damage from a creature you can see within 5 feet of yourself, you can take a Reaction to halve the damage taken. The creature takes 1d6 Necrotic or Radiant damage (your choice).
At Higher Levels
The damage increases by 1d6 when you reach Martyr levels 5 (2d6), 11 (3d6), and 17 (4d6).