Creativity is a challenging topic for artificial intelligence (AI) from the perspectives of both science and engineering. For engineering purposes, the manner in which creative AI systems provide values to humans and societies is a major concern that should be examined for the future development of AI technologies. The broader purpose of this study is to present a new direction of designing creative AI systems that consider their relationship with humans. We thus propose the basic design and concepts of a co-creative narrative generation system that produces diverse narratives through continual narrative generating chain reactions involving many agents. These agents include narrative generation programs and human narrative creators. The characteristics and significance of this design are discussed from several perspectives: 1) the relationship between generative programs and humans, 2) the design direction of narrative creativity, 3) the architectural aspect of a co-creative system for integrating many generative agents, and 4) knowledge construction in the narrative co-creation cycle.