Marcellus, along with Lazarus, Karen, and Merlin, were successful in slaying Alice XV (Fifteenth), the previous Monster Lord, but realized her intentions for coexistence too late. Just as he and his companions were proceeding to spread her wishes, Alice XVI (Sixteenth) came along and attacked the group out of blind rage upon noticing her dead mother, killing Karen and Merlin. Having killed Karen, a woman whom Marcellus and Lazarus both loved, they founded Ilias Kreuz out of vengeance.
Sometime after that, he met Lucifina and the two fell deeply in-love, and was brought out of his despair. They both had a child, Luka, and eventually Marcellus grew to no longer hate monsters and began assisting them, leading them to Enrika, a safe haven for them.
However, Lazarus eventually learned that Marcellus had helped monsters and felt that he had betrayed both the ideals of the group and insulted the memories of Karen and Merlin. Marcellus replies that Karen and Merlin would never have wanted revenge. Lazarus then vented his frustration with an easily dodgeable attack only to realize to his shock and horror that the Monster Lord's attack left Marcellus blind in his left eye; he had been unable to see the attack coming, and shortly dies afterward. With his best friend dead at his own hands Lazarus spread the rumor that monsters killed him so that a further wedge would be driven between humans and monsters, but not before giving him a proper burial at Gold Port.
Luka was originally aiming to become a martyr because of what he had heard and been told about his father, holding the belief that Marcellus was a crazed terrorist and that he in turn would be required to die to correct the sins committed by his father. He explains this to Alice XVI (Sixteenth) at Sabasa Castle, but she reassures him that the actions of a father do not extend to a child.
Once Goddess Ilias deploys her forces over the world, Lazarus tries to fight off a Trooperoid, remembering how Marcellus helped him and even saved him from a Scorpion Girl. However, instead of being saved by Marcellus, Lazarus is saved from imminent doom by Luka. Lazarus tries to atone by fighting the attacking forces, but ends up dying due to an unofficial contract with the fire spirit Salamander, leaving his body charred. Lazarus says he never really stood a chance without his best friend, and in his final words requests to be buried next to Marcellus's grave. Luka tells their graves that he will defeat Ilias.
During the final battle with Ilias, Luka sees his parents telling him to live in the world they dreamed of before delivering the final blow.
One month after Ilias's defeat and Luka recovers from his coma from the battle, he returns to Marcellus's grave, telling his father that he had accomplished his goal.