FORTITUDE
Type(s) Trait
You have a +1 bonus to your Constitution DC and Constitution saving throws due to resilience, grit, willpower, or similar effects. Bonuses provided by this ability cannot exceed the highest ability modifier you have between Con, Wis, and Cha and are halved while you're at 50% your maximum HP or less (rounded down).
Upgrade Your bonus increases to half your tier in this ability and also applies to your Charisma DC and Charisma saving throws. Round up for Constitution and down for Charisma. At tier 3+ this is superhuman.