Guts (ガッツ Gattsu) is a wandering mercenary whose entire world from birth is warfare and bloodshed. Born from a hanged corpse, the adoptive mother who rescued him dies from the plague when Guts is only three years old, and from then on Guts learns to fight in the mercenary band led by his adoptive father Gambino.
Gambino is cruel to Guts even as he teaches the boy warfare, selling access to Guts to a rapist among the mercenaries and later attempting to murder Guts in a drunken rage. Guts flees after killing his adoptive father in self-defense.
As a young man, Guts fights without any regard for his safety and earns a fearsome reputation. He catches the attention of Griffith, the charismatic leader of the "Band of the Hawk" (鷹の団 Taka no Dan).
Griffith, after fighting for a bit defeats Guts, forcing him to join the Band of the Hawk, and Guts soon becomes the band's renowned raid leader and Griffith's deadliest subordinate.
He also forms a heated rivalry, and later relationship, with Casca, the only female member of the Hawks, who is Griffith's right-hand commander. Griffith reveals to Guts that though Griffith is not a noble, he "…will get his own kingdom", and possesses a Crimson Behelit pendant—an "Egg of the King", the ownership of which destines the bearer to "obtain the world in exchange for his own flesh and blood."
Soon thereafter, the Band of the Hawk faces Nosferatu Zodd on the battlefield; this seemingly unkillable monster notices Griffith's Behelit and departs, warning Guts that his continued friendship with Griffith will result in Guts' death.
The Hawks play a pivotal role in ending the 100-year war that has ravaged the country of Midland and are initially welcomed as heroes, but Griffith's aspirations to rule his own kingdom are shattered when Guts leaves the Hawks to find his own dream, after having overheard Griffith say in private that he can only view someone as his equal and friend, rather than subordinate, if they have their own dream, rather than cling to his.
Griffith challenges Guts to a duel and is defeated almost immediately. Unable to cope with the loss, Griffith seduces the King's daughter Charlotte but is caught and ends up in the dungeon for a year, suffering daily torture.
By the time Guts learns of this and helps the outlawed remnants of the Hawks rescue Griffith, the Hawks' leader has been horribly mutilated and rendered a mute shadow of his former self.
Griffith's despair at his inability to fulfill his dream activates the Crimson Behelit. It transports the Hawks to another plane, where they encounter archdemons collectively known as the God Hand in a ceremony known as "the Eclipse".
Urged onward by the eldritch beings, Griffith sacrifices his soldiers to the God Hand's "apostles"—humans like Nosferatu Zodd who sacrificed their loved ones and humanity for power—so that he can become the God Hand's fifth and final member, "Femto". His first act upon resurrection is to rape Casca in front of Guts.
Guts witnesses the brutal slaughter of his comrades within the God Hand's domain. He and Casca survive through the intervention by the mysterious Skull Knight, a benevolent demonic being whom Guts met on his travels.
Guts loses an arm and an eye, while Casca is driven insane, and both bear an occult brand that attracts the predation of supernatural creatures every night. Leaving Casca in the care of the blacksmith Godo and Rickert, a Hawk who escaped sacrifice because he was not present at the Behelit's activation, Guts begins hunting down apostles in search of revenge against Griffith.
Guts is joined by an elf, Puck, and is later reunited with Casca as she is about to be burned as a witch in the city of St. Albion. There, encountering Farnese of the Holy See Church's Holy Iron Chain Knights, Guts endures a nightmarish ordeal that ends in Griffith's physical form restored. As Guts takes Casca to the Elven realm of Elfhelm for sanctuary with the help of his new companions, Griffith creates a second Band of the Hawk with Zodd and other Apostles among its ranks to battle the invading Kushan army.
The war between Griffith and the Kushan emperor, a rogue apostle, climaxes with the emperor's destruction and the overlapping of the mortal realm and the supernatural.
No longer challenged by demon or man, Griffith establishes his rule over Midland with the endorsement of the Pope and Princess Charlotte, creating the city of Falconia to provide the Midlanders with refuge from the ever-increasing attacks of mythical beasts, unaware their new ruler is actually one of them.
