This book explores a pivotal moment in our technological evolution, where artificial intelligence is transitioning from a functional tool into a social presence embedded in everyday life. As our interactions with technology become increasingly relational, we face a critical gap in the language, frameworks, and perspectives needed to design for these emerging dynamics. This book addresses that gap by guiding readers through a design-led journey into the future of human-AI coexistence. Grounded in the method of Research through Design (RtD), this book moves beyond abstract speculation to present three provocative, real-world case studies. Each artifact—a social media-savvy robot named Beau, a diary-keeping air purifier called Areca, and a shaman-inspired AI oracle known as ShamAIn—serves as a probe into distinct facets of relational AI, ranging from social companionship to intimate cohabitation and formal authority. Through these design speculations, this book offers not only insights but also a new way of asking questions. It provides a practical guide and a conceptual toolkit for designers, researchers, and creators to responsibly and imaginatively shape the social relationships we come to have with the intelligent things we create.