Takagi was stationed in Germany for two years and engaged in collaborative research with August von Wassermann under the direction of Paul Ehrlich at the Robert Koch Institute in Berlin. His stay was at his own expense, not at government expense, and he was roommates with an otolaryngologist, Kazuichiro Okada.

The photo from https://www.rki.de/EN/Content/Institute/History/history_node_en.html

Philippstr. 23

He married a German woman, Minna Ballerstedt, in 1904. They lived in Taipei, Taiwan until 1929.