The origin of the pentagram in this context arises in the 4th century when ancient Japanese warriors would go into battle with swords and bows. These brave men wore armor made of copper and bamboo and were very well protected. Lead by the powerful and invincible Shogun, Misutoori, these samauri won many battles and few were ever injured.
When Misutoori found steel, he modified his armor, incorporating the new material into his breast plate. He decorated the breast plate with a pentagram, a symbol of good luck. In his next battle, he was killed by an arrow to the head.
Since then, the pentagram has come to mean to all Japanese people -
modify this sucker and you're dead meat.