We describe an overview of Question Answering Challenge (QAC) 2 Subtask 3, a novel challenge for evaluating open-domain question answering technolo-gies, at the NTCIR Workshop 4. In QAC2 Subtask 3, question answering systems are supposed to be used interactively to answer a series of related questions, whereas in the conventional setting, systems answer isolated questions one by one. Such an ... [Show full abstract] interaction oc-curs in the case of gathering information for a report on a specific topic, or when browsing information of interest to the user. In this paper, first, we explain the design of the challenge. Reporting the results of the run conducted and techniques employed there, we then show that existing technologies have the potential to address this challenge.