The proliferation of online simulation games across the globe in many different languages offers Computer Assisted Language Learning (CALL) researchers an opportunity to examine how language learning occurs in such virtual environments. While there has recently been an increase in the number of exploratory studies involving learning experiences of predominantly English as a Second or Foreign Language (ESL/EFL) participants in these environments, the context of a Japanese as a Foreign Language (JFL) classrooms has rarely been examined. To address this, this study investigates a Second Language Acquisition-theory driven instantiation of CALL within the context of a JFL classroom. Through a mixed-method case study approach, participants' natural acquisition of Japanese in a 3D virtual environment was examined. Data detailing participants' communicative capacities in several modalities were collected, as were their attitudes toward participation in a massively multiplayer online (MMO)-based virtual world of Tokyo. In the present study, eight sources of data from eleven university-level JFL students (n = 11) were collected and analyzed to evaluate the learning outcomes from an integrative CALL framework (Warschauer, 2004; Yamazaki, 2014). Based on both interpretative and statistical analyses of data, the major finding of the present study was that the participants, when immersed in the 3D virtual world of Tokyo, acquired contextualized communicative competence. More specifically, quantitative analyses revealed statistically significant improvement in the participants' acquisition of incidentally encountered vocabulary, in particular, kanji pronunciation and vocabulary interpretation. Qualitative analyses revealed participants' acquisition of various communicative competencies specific to the context, including persuasive talk, concept of audience, collaborative communication, and colloquial expressions. Data from a post-hoc reflection survey provided strong evidence that most students found the course to be effective, as it made them use Japanese more than in a regular class, and thereby developed more necessary communicative skills to function in Japan. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]