Meiji Kenkaku Romantan: Daireimaku - Zenpen (S01E20)

Kenshin and the group are enjoying some tea time together. The group probes Kenshin to entertain them with an interesting story from his travels, specifically requesting "a story that's unusual, fun, and includes a villain's defeat." To answer to their demands, Kenshin decides to tell them about someone he met when he was visiting a foreign settlement in the lively city of Yokohama. A foreign doctor named Elder who was always wearing a mask. (Crunchyroll)