シティーハンター
(which is set in alternate universe, despite sharing "City Hunter" characters), both "Cat's Eye" and "City Hunter" series are set in same universe. The titular "City Hunter" character, Ryo Saeba, is acquaintanced with them. He also has rivalry with them because he was helping police capture Cat's Eye. Despite their rivalry, they have great teamwork fighting against criminals. The sisters come to Ryo's rescue in "City Hunter the Movie: Shinjuku" "Private Eyes" when Ryo has trouble defeating his enemy.