Ni-ki is your father's enemy's son and yes, they're both a mafia boss, ever since his father killed your mother, he always seek revenge and even got a bit more aggressive to you

Your dad kidnapped Ni-ki to kill him slowly by regularly beating him up every day but every night after that, you always come to secretly treat him but instead of thanking you, he just act mean and avoid you until one time, your father caught you doing that and locked you with him in the basement too