The anime series opens with Gatts arriving at a town outside a castle in Midland. However, he did not arrive in this town by accident. He has been on a solitary journey to destroy those who associate themselves with God Hand, the ones that destroyed everything that he ever cared about. Armed with a massive sword, the Dragonslayer, he pursues them relentlessly with superhuman will and stamina. Whether this is caused by the Seal branded on his neck is not known but it certainly renders him almost indestructible before his enemies. Make no mistake, however, in thinking that he has become immortal. He is still a mortal. He just happens to be able to take more punishment than any other person in the story.

After his battle with the Snake Baron, the series switches to a flashback mode to explain how he became what he is now. Here, we see Gatts as a very young mercenary going up against a rather large knight defending a fort that they have put under siege. After the siege, Gatts is on his way to another site that might require his services when he is harassed by mounted soldiers. These soldiers turn out to be members of the Hawks, a mercenary band led by Griffith. He saw Gatts's fight earlier and decides that he would make a fine addition to his army, if he can convince him to join. Needless to say, Gatts refuses the offer but Griffith gets him in a situation where the winner of their wager gets his wish. Griffith eventually prevails over him, hence making him the latest member of the Hawks. Shortly thereafter, Gatts is given command of the the Raiders, the heavy cavalry branch of Griffith's army.

The Hawks soon enters service with Midland, which is embroiled in a hundred-year long war with the Chudan Empire. They immediately prove their mettle when they defeated the seemingly invincible Black Ram Heavy Lancer Knights. This catches the attention of the king of Midland and has since led to Griffith's involvement to crucial battles, giving him and the Hawks numerous honors. However, the field commanders, many of whom belong to the aristocratic class, have grown resentful of his meteoric rise within the Midland army and thus regard him as nothing but an upstart mercenary commoner. And to one commander, Yurius, his disdain for Griffith has come the the point that he feels that is necessary to have him eliminated. But the assassination fails and at this stage of the story, Griffith's ruthlessness is revealed and proceeds to remove those who stand in his way of achieving his dream of getting his own kingdom.

All the while, with the battles and political intrigues raging around him, Gatts has been struggling to find a purpose in his life. He has been living his life according to what the other people tell him. Realizing that he too can have a dream and the freedom to pursue it and probably partly alarmed by what Griffith has started to become in his pursuit of his dream, he decides to leave the Hawks. Understandably, Griffith refuses to let him leave without a fight. To everyone's surprise, Gatts wins over Griffith very easily and thus, earns the right to leave and find his purpose in life. This event has shaken Griffith so profoundly to the core that it precipitates his downward spiral which leads to his fall from grace and eventual imprisonment. The Hawks, now a disgraced unit, is forced to flee for its own survival.

More than a year has passed since leaving the Hawks, Gatts now knows for whom he wields his sword. However, he hears news that the Hawks have been cornered and about to be routed by the Midland army. He arrives in the nick of time to save them from being destroyed. There, he learns of the fate that has befallen Griffith and the Hawks. He also learns of a plan to rescue Griffith from prison and in the dead of night, he joins a small team lead by Caska that will carry out the plan. With the help of Princess Charlotte's personal attendants, they make their way through the secret undeground passageways and into the prison tower. Upon seeing Griffith's state, Gatts breaks down and blames himself for what happened to him.

Having gotten to Griffith, they now fight their way out of the prison tower and the pursuit begins. Eventually, the castle knights catch up with the Hawks and a skirmish ensues. While they manage to defeat the pursuing knights, they realize that Griffith may no longer be capable of leading them back to respectability and are forced to think about their future as a fighting force. Meanwhile, haunted by his visions of his earlier ambitions, Griffith takes control of a wagon and takes off, sending the other Hawks scampering to get him back. A short time later, his wagon tumbles out of control and Griffith is thrown out into a shallow lake. Seeing his broken right arm, he starts laughing like a mad man. Realizing the futility of making his dream come true, he tries to commit suicide but only managed to wound his neck. Griffith looks down and sees his lost pendant, the Behelit, wrapped around his left hand. Not far behind, Gatts and the rest of the Hawks finally catch up with him while the morning sky is beginning to darken due to an eclipse.

Gatts is the first one to reach Griffith and he too notices the Behelit, this time soaking in Griffith's blood but fails to see its transformation into something that looks like a human face. Suddenly, they become enveloped and trapped in a nightmarish environment swarming with hellish monsters, as one by one mysterious beings begin to appear before them. They are collectively known as God Hand, beings regarded as "angels" and "demon kings" at the same time by those who inhabit the world of the dead and they can manipulate man's destiny on earth. It is here where God Hand tells the Hawks that Griffith is destined to become one of them and in order for that to come to pass, the Hawks are to be slaughtered as sacrificial offerings.

The Hawks try to put up a fight but in vain. Their deaths too have been pre-ordained. Gatts tries to help Caska as a swarm of monsters comes down upon her but another monster grabs his left arm, preventing him from getting to her. Then, they hear a sound that signals the birth of the new demon king. Griffith has now completely transformed into the newest member of God Hand, Femto the Wings of Darkness. He then flies down to where Caska is. Desperate to free himself from the monster's grip, Gatts cuts off his left arm with his broken sword and runs towards her. But almost immediately, the other monsters pin him down to the ground while forcing him to watch Femto rape Caska. Soon, one of the monsters' claws holding his head punctures his right eye. As blood begins to fill his vision, everything fades to black.

So ends the anime series, with the epilogue showing Gatts leaving Godo's house to seek revenge against God Hand and their minions, as we see him do in the first episode of the TV series.

Special thanks to The Black Sun Over Midland, the Berserk Shrine for this story.