Otsuji stood for election as an Independent in April 2003, at 28 becoming the youngest person ever elected to the Osaka Assembly. She later joined Rainbow and Greens, a new Japanese political coalition dedicated to developing an alternative society based on ecological politics, participatory political ideas and decentralisation. She contested the 2007 House of Councillors election on the Democratic Party of Japan list for the national proportional representation block but was not elected. However, in May 2013 when incumbent member Kunihiko Muroi, Otsuji took up his spot and became the first openly homosexual Diet member. As Otsuji did not run in the 2013 House of Councillors election, she left office at the end of the term in July.