Xiang Kexin With an aim to understand the unique roleplay affordances and constraints of AI companion platforms, our research proposes a new roleplaying game (RPG) category, “LLM-based single-player online freeform RPGs.” Through a case study of Character.AI, we develop a productive analytical toolkit – “roleplace space,” “four frames of collaborative storytelling”, and “gravity model” – that enables a critical examination of how AI companion roleplay operates in ways intrig