Chapter 7: Indestructible Physique (Passive): When your health drops to 25%, your physical defense will be "massively" increased based on your True Strength, True Agility, True Stamina, and True Intelligence attributes.
The increase amount is: True Strength + True Agility + True Stamina + True Intelligence, the total sum multiplied by 0.5 (meaning, after the Hunter currently masters this, your Strength, Agility, Stamina, and Intelligence attribute total is 1136 points × 0.5, increasing physical defense by 568 points).