When you take damage from any source, you can use your reaction to harness your spilled blood, harden it and convert it into a protective barrier. The amount of hit points you lose from the triggering damage is converted into a temporary barrier. This barrier has hit points equal to the hit points you lost, shares your damage resistances and immunities, and it takes damage before you do. If the barrier is reduced to 0 hit points, any left-over damage carries over to you.

The barrier remains active for the spell's duration or until it is reduced to 0 hit points, at which point it dissipates.