Pain Blocker makes the user unable to detect any pain, both inside and outside their body.
Gigantomachia is able to keep this Quirk active in conjunction with his original Endurance Quirk, contributing to his already extreme levels of strength and durability. This lets him easily withstand powerful attacks, while also allowing the giant to keep attacking without being halted by pain. An example of this is when he shrugged off being hit head-on by Dabi's blue flames, which are far hotter than regular fire.
Combined with his immense size, hardened muscles and ability to greatly conserve his energy and stanima, this Quirk adds to Gigantomachia’s tremendous physicality, to the point where he can plow through entire cityscapes with groups of trained warriors and Pro Heroes attacking him without exhausting from fatigue.