The oldest of the Test Tube Babies, Cain is often seen as Abel's elder twin. He was once the gentle, beloved leader of the Mars Colonization Project, until an accident killed him. Seth injected him with the Crusnik nanomachines which saved his life, but also drove him insane. In the war following the return of the colonialists to Earth, he and Abel took the side of the vampire returners. When Lilith's influence made Abel question their choice, Cain killed her. Furious, Abel and Seth confronted their brother, pushing Cain out of the space ship and into the atmosphere. His body burned into a pile of ash. Cain was able to regenerate his body from the ash, however, he sometimes has difficulty holding his makeshift body together.

Nine hundred years later, he met Isaak Fernand von Kämpfer. Together, they took over the Rosenkreuz Orden, a small, insignificant organization in Berlin that consisted of enemies of the Vatican. Through Cain and Isaak's charisma and power, the Orden grew into the world's leading terrorist organization. Cain's motivations are unclear, but he seems bent on the destroying humanity and the world. His subjects refer to him as "Mein Herr" which is German for "My Lord." He is also referred to as "Mein Herr Contra Mundi", German for "My Lord Against the World". His most popular title, however, appears to be Contra Mundi.

Once his brother Abel learns Cain is alive, Abel's primary goal becomes to kill Cain once and for all. When Cain leads the Rosenkreuz Orden on an attack of Albion, the two brothers have their first clash and Cain kills Abel with relative ease due to his higher Crusnik fusion level and Esther's sudden appearance, that distracted Abel. Realizing Abel had destroyed the control panels of the rocket, he plans to merge himself with Abel's body to get the access codes from Abel's memory. However, Abel is revived with Lilith's nanomachines thanks to Caterina and Tres. This puts Abel at the same power level as Cain and their next clash ends in a draw. Accompanied by Ion Fortuna, Abel has pledged to hunt Cain for eternity, if need be, until he is destroyed.

When his Crusnik powers are activated, Cain's lips and eyes turn red, his hands grow blue claws, he grows four white wings, and a black lance materializes in his hands. In this state, he can generate destructive red energy. When not in Crusnik form, he appears to have the power to launch a destructive and invisible force from his hands and to possess super strength. Among the four Crusniks, Cain is the only one who has fused 100% with his nanomachines in the novels, however in the anime Abel also achieves 100% fusion, without the insanity, after being infused with Lilith's nanomachines.

(Source: Wikipedia)