Virtual reality (VR) environments are increasingly being addressed by Human-Computer Interaction researchers and practitioners, due to the recent and rapid development of affordable hardware targeted to the mass market. In that respect, implicit interactions are the go-to paradigm for conceiving VR applications, particularly in simulation and gaming. However, to the best of our knowledge, there is still a significant gap in literature regarding models and practical guidelines to assist designers and software developers when building interactive applications in this domain. As a way to provide a common ground for designing interactive applications in VR environments, this paper presents a formal conceptualization of implicit interaction mechanisms. To do so, we propose a set of formal models and we show a working example implementing such interaction mechanisms in an interactive visual novel, i.e., a video game comprising a compelling narrative extended by the interaction within an immersive environment, which in this case corresponds to a VR world. As a way to gauge user acceptance of the produced video game, we conducted a controlled user study measuring perceived immersion and player experience with a particular focus in the implementation of the proposed implicit interaction mechanisms. The obtained results are highly promising, highlighting the understandability and flexibility of the proposed mechanisms.