Human-computer interaction (HCI) researchers have explored designs that connect humans and non-human beings based on post-humanistic discussions on speculative ethics of care regarding more-than-human worlds. Following these empirical and theoretical frameworks, this paper explores the potential of HCI design to foster human affective emotion toward fermentative microbes. We present the design process for the Nukabot, which is a technologically enhanced traditional Japanese wooden bucket used to pickle vegetables using lactic acid bacteria; the Nukabot is able to have conversations with humans via voice interaction. We describe the ethnographic accounts of six participants who spent 10 days taking care of, talking to, and being addressed by the Nukabot. We analyze their experiences through three ethopoietic elements of care: maintenance, affection, and obligation. Finally, we discuss the design implications of the Nukabot and its contributions to HCI research.