This paper provides a summary of our ongoing project for providing integrated access to Japanese multiple digital libraries, archives, and museums. The main goal to construct a federated searching system for Japanese humanities databases, which searches multiple databases in parallel and provides on-the-fly integration of the results, has required the system to deal with heterogeneous metadata schemas in various formats. In this paper we discuss the metadata-related challenges faced at the front-end for retrieving multiple Japanese databases in parallel and integrating bilingual retrieved results. Aggregation and integration of the retrieved results in English and Japanese are complicated if a search needs to be performed from multilingual sources.