## 3 Materials and Methods
### VR Intervention Design  
We developed a VR prototype application that delivers a social story in the format of an interactive visual novel. The VR environment, created with the Spatial.io platform and Unity 3D ver. 2021.3.21f1, consisted of two linked virtual scenes themed around the daily life of a child named \"[PERSON]\" The first scene, entitled \"[PERSON]'s World\", represented a home setting specifically, [PERSON]'s bedroom (Figure 1), and the second scene represented a school setting entitled \"[PERSON]'s School\" (Figure 2). These scenes were populated with familiar objects such as toys, furniture, a classroom environment, etc., to make the experience relatable and to simulate real-world contexts. The application was designed to run on a standard PC, representing a non-immersive VR setup. In this context, non-immersive refers to the absence of head-mounted displays or sensory isolation, offering instead a screen-based interactive experience (no VR headset was used, for ease of integration in the school setting). The environment followed a desktop-based VR format, including interactive 3D scenes, dialog, and narrative decision-making features consistent with non-immersive VR used in educational contexts. The dialog and text within the game were in Greek, the native language of the participants and their teachers, to ensure accessibility and comprehension. The educational content of the intervention was centered on teaching appropriate social greetings and fostering empathy. The storyline followed a day in the life of [PERSON], a virtual character who models both appropriate and inappropriate social behaviors. For example, if someone greets [PERSON] by saying \"hello\" and [PERSON] responds by saying \"hello\" back, this is considered an appropriate social behavior. At the start of the VR experience, in [PERSON]'s virtual bedroom, a friendly guide character welcomes the player (the child) and provides instructions for how to proceed. A prominent visual overview (the \"Big Picture\") is presented to outline the session's goals and steps, helping the child understand what  
Figure 1: Virtual environment “[PERSON]’s World” on Spatial.io. Figure 2: School environment with visual indicators on the floor. will happen next. The child can interact with various items in the room. For example, clicking on a computer in the virtual bedroom plays a short video demonstrating how to greet someone politely, emphasizing saying \"hello\" and making eye contact. This acts as a video-based social story, showing a scenario of [PERSON] greeting a friend. Next, the player clicks on a bookcase, which opens a written version of the same social story about greetings. Presenting the lesson in both video and written formats reinforces understanding and caters to different learning preferences. After reviewing these materials, the player clicks on a door, which transitions the VR scene from [PERSON]'s home to his school. In the \"Peter's School\" scene, the player is engaged in a virtual school environment with classrooms and hallways. The character [PERSON] appears as a guide within this scene; he introduces himself to the player and explains the next interactive task. The player is guided along a path marked by visual indicators on the floor, leading to the next interactive activity (Figure 2). Upon reaching a specific spot, indicated by a highlighted area or circle in the virtual schoolyard, the player is presented with a situation and a set of response options (Figure 3). For instance, the scenario might involve [PERSON] encountering a classmate and the player must choose how [PERSON] should respond (options could include a proper greeting, an improper greeting, or ignoring the classmate). These choices are presented as text or icons on the screen, and the child must select an option.