TOKYO — As protests were spreading around the globe in response to George Floyd’s killing by the police, Sierra Todd, an African-American undergraduate in Japan, organized a march last month in Tokyo to show agreement with American demonstrators. She said she hoped it would prompt Japanese marchers to think about racism in their own country, too. “Of course, we want to talk about American issues, and Black Lives Matter is an American thing,” said Ms. Todd, 19, who is studying at Temple University’s campus in Tokyo. “But we also do live in Japan.”