Karthus and Vladimir relations.

They have pretty much the same outcast trope of childhoods.

One loved the act of murder, the tone and quality of blood and the adrenaline rush.

• A day earlier, the teenaged Vladimir had brutally murdered two boys of his age, for no better reason than to enjoy the intoxicating scarlet bloom that surged forth. He realized immediately that he would never be able to suppress his murderous desires, and if he remained in Noxus, his foul deeds were sure to catch up with him. Without hesitation, he abandoned the city-state, and journeyed south.

The other loves the unlife after death.

• Even as a boy, Karthus was different. There was a darkness within him that could not be denied. The young child clung to the shadows and shunned the company of others. He snuck into the funerals of strangers, and spoke to their tombstones in the cemetery. He sought out corpses of animals to preserve and memorialize them, creating a grim collection of morbid art. Karthus volunteered to tend to the sick and dying, though his intentions were not to help, but to closely witness the passing of those who were beyond help. Ultimately, he went so far as to elaborately stage his death, and he secretly observed his own funeral with intense fascination. When others discovered what Karthus had done, they were so shocked and disturbed that, in a way, he became truly dead to them. Karthus found himself fully rejected by the living.

They are so perfect for each other.

There needs to be a skin that embraces their tandem personality. One character is of movement and the painful surge of blood seeping from one's body with the intoxicating and stimulating pleasure of life, leeched from your victims. The other character is a hollow siren of ethereal destruction and hurried death. Death is rejoiced not with the silent, soothing, blood rushing feeling of pleasure but with the melodic haunting and screaming voices of the dead.