Marcellus is Luka’s father, Lucifina’s husband, and Heinrich’s descendant. He had slain Alice XV (Fifteenth), the previous Monster Lord, along with Lazarus, Karen, and Merlin, 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. 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. Lazarus executed him and spread the rumor that monsters killed him so that a further wedge would be driven between humans and monsters.
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.