The kalasag (lit. Shield of Aptitude)is the fifth weapon of the Bakal na Krus. It has no official name, as Juan concludes that the name of the weapon is not important or at least too preoccupied on saving Pikoy, who is currently trapped in Homonhon at that moment. According to historical records, Juan is the first Tagabantay to unlock the weapon. The shield is used to protect the user from attacks and forms a protective blue aura range. The shield was shown to deflect gun bullets. It is also used to repel or reflect any kind of physical attacks.
The Kapatiran never thought that the bakal na krus possesses a hidden armor. It was unleashed when the kapatiran was trying to have a gun fight from aswangs hiding on a cargo boat. Asiong was about to be hit by a bullet when Juan accidentally unleashed the armor, while trying to cover his best friend. No one ever taught Juan how to unleash it. This only means that a student can sometimes learn from itself, even without it's master's words.