Start with the Libraries Search Engine, OneSearch. You can type in any language, romanized or in the vernacular script.
Example: See the record for Aizawa Seishisai. One of the related individuals is Fujita Tōko, but you'll have to do some investigating to learn that he was a mentor of Aizawa. The Associated Subjects section at the bottom reveals more about the author, and the links there will search WorldCat.org for materials that are described with the same subject. Generic subjects like Politics and government and Diplomatic relations won't yield much, but more specific terms like Mitogaku (水戸学) and Shinron (Aizawa, Yasushi) connect to meaningful materials that will help advance your research.