The metaverse is a vast virtual space made up of many distinct virtual worlds, each with its own purpose and characteristics. Among them, there is a type of virtual world that incorporates digital twins. In these worlds, each digital twin acts as an interface bridging the virtual and physical worlds, enabling two-way interaction between virtual objects and their physical counterparts. This allows information from physical objects to synchronize with their virtual versions. Conversely, controlling virtual objects can affect the physical ones. By analyzing service scenarios, key requirements can be identified, which serve as the basis for developing an integration reference model. This Recommendation defines a reference model for integrating virtual and physical worlds through digital twins in the metaverse.