I am writing this paper as a member of the indie team named Belirian, where I held the position of game and story designer and writer, as well as a student of cultural studies. Belirian is a five person team: programmer, 2D artist, two 3D modelers, and myself as story designer. Together, we are creating a video game based on ancient Slavic myths. In this dissertation I will draw out the foundations of the fictional world and narrative for our game. Using these foundations, we hope to finish the game by 2021. Due to the requirements for this dissertation, as well as creating these foundations, it was necessary to conduct research into Slavic myths and beliefs, and then adjust them to the media of video games where knowledge of video game theory was needed. In terms of video games theory, I have mostly referred to Jasper Juul and his book “Half-real”, while for my research into ancient Slavic beliefs and myths, I have mostly used the works of Radoslav Katičić and his series of books named “Tragovima svetih pjesama naše pretkršćanske starine”, together with Vitomir Belaj and his book “Hod kroz godinu”. This dissertation consists of three main parts. The first part starts with a description of video game theory, ancient Slavic myths and elements of these myths that will be used in the game. The first part also includes a short description of the game’s narrative. The second part considers spatial relations in the fictional world and one feature of this, which is its connection with elements of ancient Slavic myths like Perun's hills and Veles's swamp or Belaj's sacred triangle. Special attention has been given to the swamp, which is the starting position of the game. The third part is based on the two main characters: the mythical hero Selev and the village Žrec, and Selev's mentor Evayna. In this paper I am submitting the first version (first zone) of the game I am writing about, which has the working title: “Son of Iraj”.