Soon, voice assistants might be able to engage in fully-fledged social conversations with people, rather than merely providing a voice-operated interface to functionality and data. So far, not much is known about designing such "social" voice assistants and the potential social experiences, which could and should emerge in everyday situations. In the present paper, we created a design fiction to explore a sophisticated social voice assistant in the context of the car. Based on models from psychology and psychotherapy, we designed the fictional "virtual passenger" Kiro. We created a website for Kiro (http://www.heykiro.com/), distributed it, and collected responses in various ways (e.g., comments). We further ran a market research-type focus group. In general, we found people to accept Kiro as a conversation partner but not as a replacement for human-human conversations. We suggest designing social voice assistants in a way to enable novel types of socially fulfilling, yet distinct human-machine conversations.