Gatsu is a boy, born of a woman after being hanged for heresy. Found by an army of mercenaries led by Gambino, age 3 Gatsu witnesses the death of his adoptive mother, crushed by the plague. It immediately began to fencing and fighting techniques, always using a sword too big for his age and showing great talent and potential. Gambino, who has always believed Guts responsible for his misfortunes, one night drunk goes into the tent of the boy in order to kill him, but he died at the hands of the boy who accidentally tried to defend themselves in some way. Gatsu escapes from the camp, and begins to live only gaining as a mercenary. In this environment, the boy stands continually among other soldiers, concerning his extraordinary fighting skills, his incredible brute strength and his sword in size considerably larger than ordinary. From then on we will see the events leading the protagonist to join the army of Griffith, the army of the Hawks, their unstoppable rise of a degree earned with success on the battlefield, and then arrive key episode that will bring Gatsu to become the Black Warrior (anime is called Knight of Darkness).