Yin and Yang are twin sisters, nicknamed by their adoptive father.  Of the two sisters, Yin was always more prone to rage and outbursts.   Yin never knew her biological mother, as she died when Yin was young.  When she was a slightly older child, her father was assinated by a killer named Apple Blossom.  Boss Kazazumi saw potential in the twins and adopted them as his own.  Yin’s home life became stable and loving, but she always felt she had a large debt to repay her father.  She learned how to be an effective killer for her father.     Eventually, Yin caught up with Apple Blossom and kidnapped her.  Without her father or her sister’s knowledge, Yin tortured the assassin to death through tickling.  She had formed a kind of tickling bloodlust after that first experience, and enjoyed subjecting enemies to the humiliating execution.   Yin’s bloodlust unfortunatley ensnared Agent Succubus, whom Yin killed through intense tickle torture, stopping Agent Succubus’ heart.  Yin was later captured by the Agency and is under house arrest to pay for her crimes.