The potential power of augmented reality (AR) makes it possible to change the semiotic meaning of the real space, and strongly influence human attitude and behavior for achieving a better lifestyle. Typical AR approaches can simply integrate computer-generated (CG) virtual images on the real space from a spatial aspect. This approach limits the potential power because only some objects in the real space can be enhanced. In contrast, virtual reality (VR) technologies make it possible to create a new fictional, but realistic virtual space by using 3D models of real persons and landscapes. In this paper, we propose a new concept named Alternative Reality that is used for building a new type of ambient intelligence experiences. Alternative Reality makes it possible to connect the real space with the virtual space temporally and to integrate the two spaces seamlessly, where its virtual space consists of real landscapes and persons not fictional ones to change the semiotic meaning of the real space and strongly influence human attitude and behavior. However, the virtual space does not reflect the events that actually happened in the real space; this means that it may be possible to enhance the real space by showing fictional events among real events. For demonstrating the Alternative Reality concept, we have developed a case study named Fictional Future, where the virtual space is constructed with fictional events performed by real persons in real landscapes. We conducted a user study of the case study to show the feasibility of the Alternative Reality concept. The user study shows that Alternative Reality augments the real space effectively and a user still experiences the virtual space as in the real space.