Viruses can explore the limits of genome minimalism by exploiting other viruses. For example, satellite viruses rely on the polymerase of a helper virus for replication. Zhang et al. describe a capsidless single-stranded RNA (ssRNA) virus, yado-kari virus 1 (YkV1), that is trans-encapsidated by a co-infecting double-stranded RNA (dsRNA) virus, yado-nushi virus 1 (YnV1). YkV1 has a single protein, an RNA-dependent RNA polymerase (RdRp), whereas YnV1 has both an RdRp and a capsid protein. Although the YkV1−YnV1 interaction shares similarities with helper−satellite systems and the other known example of trans-encapsidation, it represents a novel lifestyle in important respects: YkV1 and YnV1 have different genome types; replication occurs inside the trans-capsid; and the interaction is cooperative, as YkV1 boosts YnV1 production. The authors speculate that YkV1 is an evolutionary intermediate destined to become an independent dsRNA or ssRNA virus.